Mika Hakkinen's victory at Sunday's United States Grand Prix typified what has become a watershed season in Formula One. Once again it would be Michael Schumacher versus Hakkinen, Ferrari versus McLaren. Instead, the 2001 season will stand as a clear divide between two very different eras, in several different ways.

Mika Hakkinen's victory at Sunday's United States Grand Prix typified what has become a watershed season in Formula One. Going into the season, there seemed little prospect of change at the top - once again it would be Michael Schumacher versus Hakkinen, Ferrari versus McLaren, and the rest of the field squabbling for the minor placings. Instead, the 2001 season will stand as a clear divide between two very different eras, in several different ways.

Hakkinen's victory was so typical of how fate confounds the best laid plans. On Sunday morning, after news of his relegation to the second row of the grid following a pitlane infringement, Hakkinen snapped uncharacteristically, citing his penalty as one of the many reasons why he decided on a year-long sabbatical from the sport. Barely two hours later, the stunned Finn couldn't find the words to express his relief and joy at an unexpected victory.

Mentally, the win was a mixed blessing for Hakkinen. The plus side is that he'll leave the sport knowing that he still has the skill and smarts to beat anyone on his day. On the minus side, he must now be wondering if his decision wasn't too premature, and mandated more by frustration than a genuine loss of dedication or interest. No matter, for the die is cast, and Hakkinen himself must know that his chances of a triumphant comeback are extremely slim.

Both Niki Lauda and Alain Prost returned to Formula One after similar sabbaticals, and both won World Championship titles on their return. The difference is that Lauda and Prost both returned to plum drives in dominant cars with inexperienced teammates as the main opposition. Hakkinen won't have that luxury, if he decides to return at all. Barring success at Suzuka in two weeks time, Hakkinen's twentieth GP win looks sadly as though it could also be his last.

Hakkinen's situation is indicative of the natural ageing process that is defining the turn of the era. The last watershed year was 1994, when Ayrton Senna's death ended the reign of the 'old guard' - Senna, Prost, Mansell and Piquet, and heralded the new era of drivers including Schumacher, Hill, Villeneuve, Hakkinen, Coulthard, Alesi, Frentzen, Irvine and Verstappen.

At the start of this season, all but Hill were still active, senior and competitive team leaders who could be counted upon to spearhead their teams' challenge for WDC glory. While they still have the consistency and experience to rack up more points over a season than their younger teammates, they've virtually all lost a precious tenth in all-out one-lap qualifying speed.

Arrows' Jos Verstappen has been outqualified 9-7 by rookie teammate Enrique Bernoldi, Pedro de la Rosa humbled Eddie Irvine for a five GP streak pre-Indianapolis, and the under-rated Jarno Trulli's pace has ousted both Heinz-Harald Frentzen and Jean Alesi at Jordan. For all his ageless passion and charm, Alesi's options for 2002 look very limited indeed, and Jacques Villeneuve has become increasingly jaded and disillusioned at BAR. With Hakkinen's and Hill's fate already sealed, that leaves only the two Ferrari drivers and David Coulthard from the 'class of post-94'.

After a very shaky start to the year, Rubens Barrichello has come on strong during the second half. But as long as he has Michael Schumacher as a teammate, the Brazilian is aiming for second at best. McLaren's David Coulthard has lasted the distance of an eight-year career surprisingly well, particularly considering that he has only ever had two teammates - both World Champions and both more experienced than the Scot. Yet, discounting a rookie season under extremely difficult conditions at Williams in 94, Coulthard has averaged only 12 points per season less than his illustrious teammates.

In 2002, Coulthard will enter uncharted waters, as McLaren team leader with a teammate who will be entering only his second season at the top level. Even with Kimi Raikkonen's much-vaunted reputation, Coulthard will be expected to outperform the young Finn. If he doesn't, Coulthard could slide into F1's obscurity.

That leaves Michael Schumacher. Just a few races ago, it would have been unthinkable to suggest that Michael Schumacher had lost even a shred of his legendary commitment to his art. Yet, for the second race in succession, he was outperformed by a teammate that is simply not in his league - and he didn't seem to mind a bit. There are mitigating factors of course. With the Championship already sewn up, and the unsettling events in America, Schumacher has justification for not performing at his peak. It could even be argued that he has deliberately held himself back to ride shotgun for teammate Barrichello. Yet none of the three reasons seem entirely believable; it is simply not in Schumacher's mindset to race at anything less than 100%.

During the week, Ferrari technical director Ross Brawn disclosed that there had been talk about Schumacher retiring. Although the prospect was quickly quashed by all concerned, the significance lay not in the possibility of his retirement but instead in the mere act of talking about it. Talk of retirement, however glib, is preceded by consideration of retirement, and that consideration in itself means that the driver concerned is not focused exclusively on the job at hand.

Montoya's pass on Schumacher at Indianapolis, combined with Schumacher's comments about the pass in the post-race interviews, belie the German's current attitude to racing. A couple of years ago, a pass like Montoya's would have drawn disdainful and supercilious response from Schumacher. On Sunday, both on the track and after the race, the German showed mellow maturity in handling the inevitable.

The pass was so reminiscent of the early exchanges between Senna and Prost at McLaren, where the Frenchman's maturity and experience often yielded to the fierce aggression of Senna's onslaughts. Prost used his legendary mechanical sympathy, tyre-conserving style and a light touch on the turbo boost button to fight Senna on his own terms.

Schumacher has his own weapons, not least his relentless consistency, wet weather supremacy and the Ferrari's almost flawless reliability. Like the latter-day Prost, though, he has shown a reluctance to indulge in the sort of wheel-banging do-or-die antics that marked his youthful battles with Damon Hill and Jacques Villeneuve. It's a sensible option, but F1 has never been a sensible sport and life-endangering risks are part of the game. When winning means taking more risks than he'd like, Schumacher will succumb like the rest of his peers. It's doubtful he'll race beyond his current 2004 contract, if he even lasts that long.

Indianapolis 2001 also marked the end of an era off the track. For anyone who receives the ITV feed, there is only one 'voice of F1' - Murray Walker. Although he was never the most technically insightful commentator (he had ex-F1 drivers to fulfil that role), Murray had unrivalled passion, his unique excitable style, and an endless succession of commentary gaffes that often proved more entertaining than the racing itself.

In a sport characterised by physical prowess, Murray Walker also excelled in his own way. For a man in his late seventies to suffer the rigours of almost year-long globe-hopping, and yet never waver in his commitment or enthusiasm for his work, is truly remarkable. Thank you and God bless, Murray Walker.

The Formula One that Murray Walker leaves will be very different to the sport that he joined. The independents have mostly gone, replaced by the corporate ethics and sensitivities of major auto manufacturers. The sport is safer than ever before, and is technologically light years ahead of where it was even five years ago. Global exposure and the rewards of sponsorship and endorsements have reached unprecedented peaks. And, as always, one era of driving superstars must inevitably give way to the next.

If Juan Pablo Montoya emerged as the only legitimate pretender to Michael Schumacher's throne, that would be cause for concern. But the sport is literally bursting with talent at the moment. Jarno Trulli, Nick Heidfeld, Kimi Raikkonen, Jenson Button and Fernando Alonso are all poised for greater glory, and it's still not too late for Ralf Schumacher or Giancarlo Fisichella to emerge as rightful champions. For the meantime, though, there is still the Japanese Grand Prix at Suzuka in two weeks - and the chance for Mika Hakkinen to score one last hurrah for himself, and for the Class of '94.