Mercedes' Lewis Hamilton passed title rival Max Verstappen with six laps to go on Sunday to win the 2021 Formula One Spanish Grand Prix in a brilliant comeback drive.

Starting the race from pole position, Hamilton lost the lead at the first corner to the fast-starting Verstappen of Red Bull, who managed to keep the Briton at arm's length for much of the contest.

Sensing that Hamilton would not be able to get close enough to attack Verstappen on track, Mercedes called Hamilton in for a second pitstop on lap 43, costing him around 20 seconds but crucially giving him fresher tyres with which to hunt down the Dutchman.

In an intriguing tactical battle, Hamilton made inroads into Verstappen's lead and duly passed the Dutchman on lap 60 of 66 to take his third win in four races so far in 2021.

"I was just hunting," said Hamilton afterwards. "I was so close for so long and I didn't think I was going to be able to make the tyres last. But I just managed to. It was a long way to come back from 20-odd seconds back, but it was a good gamble, a really great strategy from the team."

"I was about to have a shot at getting past him before I pitted and I was really conflicted. Do I come in or I do ignore the call and stay out? Obviously I did what the team asked and naturally that's because there's a great trust between us. Just a remarkable job by everyone in this team. What a day."

Despite having led the majority of the race, Verstappen took a phlegmatic view of Hamilton's triumph.

"In a way, I could see it coming," said the Dutchman, who at least took the bonus point for fastest lap. "At the end, with the softs, he was faster, and then when we were on the mediums he clearly had a lot more pace, he could just stay within one second."

"There was not much we could have done. They went for another stop and then I knew it was over because I was already struggling with the tyres and you could see every lap he was getting closer and closer. I was just a sitting duck. We were just clearly lacking pace. I tried everything I could."

Hamilton's teammate Valtteri Bottas finished third, though the Finn might have drawn the ire of his team by not letting Hamilton overtake him as easily as he might have done on lap 52.

Behind the top three, Charles Leclerc took a fine fourth in his Ferrari, with Verstappen's teammate Sergio Perez in fifth and McLaren's Daniel Ricciardo sixth.

Leclerc's teammate Carlos Sainz was seventh, ahead of the second McLaren of Lando Norris and Alpine's Esteban Ocon. AlphaTauri driver Pierre Gasly rounded out the top ten.

The only driver to fail to see the chequered flag was Gasly's teammate Yuki Tsunoda, who stopped on lap 7 with a mechanical issue.

Hamilton's win sees him extend his lead in the drivers' championship to 94 points. Verstappen lies second with 80 points, with Bottas third on 47.

In the constructors' standings, Mercedes lead the way with 141 points. Red Bull stay second with 112, and McLaren are third on 65.

The fifth round of the 2021 F1 season is the Monaco Grand Prix on May 23.