Mercedes driver Lewis Hamilton won his 100th Grand Prix and retook the lead in the 2021 Formula One world championship in Sunday's dramatic Russian Grand Prix, after long-time race leader Lando Norris slid off track during a late rain shower.

The changing conditions also helped Hamilton's title rival Max Verstappen finish second, after he started last following a penalty for exceeding his season's allotted total of three engines.

With Verstappen's Red Bull starting from the back, Hamilton knew he had a great chance to eat into the Dutchman's championship lead, but a poor start saw him fall from fourth to seventh on lap one as Carlos Sainz and Norris set the pace up front.

Poleman Norris looked the quicker of the two, and the McLaren driver took the lead from Sainz's Ferrari on lap 13 and began to pull away at the front.

Once all the different pit strategies had played themselves out, Hamilton had worked his way up to second behind Norris by lap 38, but just as in the preceding Italian Grand Prix, McLaren seemed to have just enough to keep Mercedes at bay, and Norris appeared set for a fairy-tale maiden Grand Prix win.

However, everything quickly changed with the arrival of a rain shower six laps from the end. While Norris elected to brave out the slippery conditions on his slick tyres, Hamilton and many others chose to dive into the pits for treaded rubber.

As the rain intensified, it became apparent that Norris had made the wrong call, and after the McLaren slid off in impossible conditions on lap 51 of 53, Hamilton assumed the lead and stayed there to take his 100th Grand Prix win.

"It's taken a long time to get to 100 wins, I wasn't even sure it would come," said Hamilton. "The team made such a good call at the end. I didn't want to let Lando go. I'm incredibly grateful to everyone here and back in the factory."

A former McLaren driver himself, seven-time champion Hamilton also paid tribute to Norris. "Lando did such an amazing job, he had such incredible pace. He's doing such a great job for McLaren - this was bittersweet. It's nice to see my old team ahead."

Behind Hamilton, Verstappen was another to take advantage of the changing conditions, timing his own tyre switch perfectly to vault from seventh on lap 48 to second by the flag, and the Dutchman was pleased with the damage limitation to his title hopes.

"It was pretty tricky on the in-lap to make the call to go inters. If we had come in one lap earlier we would have destroyed the inters in the last sector. But, of course, to come from last to second is very, very good. When I woke up this morning I definitely didn't expect this result."

Sainz rounded out the podium places after a strong finish, with Norris' teammate Daniel Ricciardo taking fourth. Hamilton's teammate Valtteri Bottas finished fifth, ahead of Alpine's Fernando Alonso.

Norris' late mishap saw him drop to seventh, though the Briton may yet receive a time penalty for crossing the white line as he struggled for grip entering the pit lane. The bonus point for fastest lap will be scant consolation for the McLaren driver, who had looked serene in the lead until the heavens opened.

Alfa Romeo's Kimi Raikkonen scored his best result of the season with eighth place, Verstappen's teammate Sergio Perez dropped to ninth in the closing stages after running third before the rain, and Williams' George Russell rounded out the top ten.

Hamilton's win sees him retake the lead in the drivers' championship with 226.5 points, but Verstappen is only two points behind, and in a further twist to an enthralling title battle, Hamilton is expected to have to take an engine penalty of his own before the season is out.

In the constructors' standings, Mercedes remain top with 397.5 points. Red Bull stay second on 364.5, with McLaren third on 234 points.

The next round of the 2021 F1 World Championship is the Turkish Grand Prix in Istanbul on October 10.