Unfulfilled talent? Two-time champion Alonso clocks up 400th F1 race
To the two-time world champion, it is a sign of his undying love for his sport and devotion to Formula One in particular even if, to his fans and admirers, it is a reminder of a great talent unfulfilled.
"To reach 400 now is a big number," said Alonso, who has admitted that travelling to 24 races a season is demanding but that he "pays off all the sacrifices" when he climbs behind the wheel of his Aston Martin.
"Knowing that no-one has reached that number in the past, it just demonstrates my love for racing, for F1 and how much I enjoy this lifestyle and motor racing in general."
To many, the Oviedo-born Spaniard is the greatest driver of his generation, a man with an unequalled talent for speed and racing, but also someone with a knack of choosing to move to the wrong team at the wrong moment in his career.
"I would love to race half of the 400 and win one more championship, or to win more races," he said. "That's the important statistic you want to achieve."
His sometimes self-effacing humour and individuality, coupled with a swashbuckling style on track, earned him great admiration as soon as he made his first appearance for Minardi at the 2001 Australian Grand Prix.
He kept his personality as he progressed to two world titles with Benetton, in 2005 and 2006, under the guidance of his manager Flavio Briatore.
Since then, despite moves to McLaren and Ferrari, a third championship has eluded him. The last of his 32 wins came 11 years ago at his home Spanish Grand Prix with Ferrari.
It was his misfortune that sometimes his personality made him a difficult team-mate, notably at McLaren with a young Lewis Hamilton in 2007, and at times with Ferrari and McLaren again in a second spell.
Thought '2009 final year'
His break from the intensity of F1 to race at Le Mans and in the Indy 500 gave him a new sense of perspective that he carried into Alpine and then Aston Martin, showing his talent was undimmed by age.
Looking back at his debut season, Alonso admitted: "I didn't have a clear road map for my career. I didn't know the next race or my next team. I was just improvising. Every week was a new adventure."
Heading into his record landmark weekend in Mexico, he also admitted he had expected to retire from F1 in 2009 at the end of his three-year contract with Ron Dennis's McLaren.
"When I won the championship in 2006 and then I joined McLaren, I had a three-year contract for 2007, 2008 and 2009 and I was 99 per cent sure that 2009 would be my last F1 season.
"That was my clear plan in my head," he told the "Beyond the Grid" podcast.
That it did not happen is part of the Alonso story –- a tale of huge talent, unrivalled race-craft and a competitiveness that, at 43, enabled him to stay on the pace and sign a new deal with Aston Martin to work with incoming star designer Adrian Newey next year.
Fellow-Spaniard Carlos Sainz, of Ferrari, is one of many drivers to have paid tribute to Alonso this week.
"It makes me think that I've done 200 so to put another 200 on top is a lot," he said.
"I just wish him to enjoy this race and especially to keep going because he's still in a very good shape and still driving at a very good level."
Hamilton, a seven-time world champion, has entered 351 Grands Prix and is second behind Alonso on the list.
"I don't know, but I might catch him up," he joked.