It is the second win of the season for the seven-time world champion following his success at Silverstone earlier this month and the 105th of his Formula One career.

It was also the third Mercedes victory in the last four races following a poor run of results in the last two years although they initially thought they had wrapped up a compelling one-two.

McLaren's Oscar Piastri was elevated to second with Ferrari's Charles Leclerc moving up from fourth to third.

The 26-year-old Russell, who started sixth on the grid, produced a stunning performance on the track, the only driver to opt for a one-stop policy that saw him nursing his second set of tyres for 34 of the 44 laps.

He was able to hold off Hamilton and the flying McLaren of Piastri, who finished third, to claim what he thought was his third grand prix victory.

His joy, however, was short-lived as a technical report released after the race said Russell's car had been found to be 1.5kg below the minimum weight limit for car and driver combined.

"Car 63 is disqualified from the race classification," the stewards announced in a statement.

"All other drivers move up in the classification," they added.

Russell's car was initially weighed at 798kg, which is exactly on the minimum weight limit for car and driver combined.

But stewards found it had not been fully drained of fuel and when it was weighed again it registered 796.5kg.

"Heartbreaking," Russell said on social media.

"We came in 1.5kg underweight and have been disqualified from the race.

"We left it all on the track today and I take pride in crossing the line first.

"There will be more to come," he added.

Leclerc, who started on pole position, crossed the line in fourth ahead of three-time world champion and series leader Max Verstappen of Red Bull, Lando Norris in the second McLaren and Carlos Sainz in the second Ferrari.

They were followed by Sergio Perez, who started second, in the second Red Bull, two-time champion Fernando Alonso of Aston Martin and Esteban Ocon of Alpine.

- 'Fantastic' -

After Saturday's deluge, the race began in bright, warm and dry conditions.

Leclerc enjoyed a smooth start from pole as Hamilton beat Perez to take second into La Source, where they battled wheel to wheel.

Norris had a poor start and ran through a gravel trap, falling to seventh behind Russell and Sainz as the early order settled while Verstappen gained two places to rise to ninth, having started 11th due to a 10-place penalty for taking an additional new engine.

Hamilton's pace took him within reach of Leclerc on lap three when, using Drag Reduction System (DRS), he swept into the lead on the Kemmel Straight.

He stayed there and by lap five led Leclerc by a second ahead of Perez, Piastri and Russell with Sainz sixth, the only top 10 driver on hard tyres, ahead of Norris and Verstappen.

Russell and Verstappen came in after 10 laps, both switching from mediums to hards and re-joining in 13th and 14th respectively before Hamilton, Perez and Piastri pitted one lap later.

Norris finally pitted on lap 16, rejoining eighth behind Verstappen with whom he battled until the end of the race.

With all of the other contenders pitting a second time, Russell became the fifth race leader and opted to stay out on the one-stop strategy.

Hamilton closed but instead of waving his teammate through, Russell was given the all-clear to race him, a potentially dangerous strategy from Mercedes as Piastri quickly closed on them.

With five laps to go, Hamilton was two seconds behind Russell and Piastri 5.4 adrift, the top three setting up a grandstand finish that saw Piastri close up to within two seconds while the Mercedes men tussled to the flag.

"We had such a disaster on Friday when the car was nowhere," said Hamilton.

"We made some changes and it was difficult to know in the wet yesterday, but the car was fantastic."

Verstappen still leads the championship race with 277 points, 78 clear of Norris. Red Bull top the constructors' championship 42 points ahead of McLaren.

Formula One now heads into a summer break with the next race in Zandvoort for the Dutch Grand Prix on August 25.