Russell’s car was found to be 1.5 kilograms underweight during routine post-race scrutineering, leading to automatic exclusion from the results.
The Briton emerged as a surprise winner from the race after blindsiding Hamilton and the rest of the frontrunners by making just one stop in what had widely been expected to be a two-stop race.
The strategy, driven by both driver and team after his first tyre change on lap 10 of 44, got the Briton out of the tightly congested field and into clear air, where he was able to maximise his pace and massage the tyres to the finish.
It forced a thrilling conclusion to the grand prix as Hamilton realised that this teammate was set to win a race he thought he’d been comfortably controlling.
The seven-time champion aced his start from third on the grid to run Sergio Pérez, launching from second, side by side through the La Source hairpin.
They jostled for position down the hill into Eau Rouge, where the Mercedes car nosed ahead and forced the Mexican to yield.
It set Hamilton up to pursue pole-getter Charles Leclerc for the lead on lap three, making an easy slipstream pass down Kemmel straight.
In clear air the Mercedes was unexpectedly rapid. The team had made some blind set-up changes after an uncompetitive Friday practice. A wet Saturday had obscured their effectiveness, but in the dry on Sunday Hamilton was able to stamp his authority on the field.
Russell, meanwhile, was having a more difficult time in fifth, up from sixth on the grid, where he was struggling to get the most from his car in dirty air.
The team made the early call to pit him at the end of lap 10. Extracted from traffic and now on the hard tyre, which turned out to be the quickest on the day, Russell felt renewed, and he encouraged his team to leave him out until the end. The Mercedes pit wall agreed, forecasting that fifth would be his best finish with or without another stop.
Hamilton had a similar feeling at the front of the field, but with victory on the line, Mercedes was less willing to risk it. When Leclerc, then second, stopped on lap 25, Hamilton was called in to prevent an undercut on a day overtaking was more difficult than anticipated.
It proved fateful to his race. While he stayed ahead of Leclerc and could keep the fast-finishing Oscar Piastri at bay, it gradually dawned on him that Russell’s pace at the front was strong enough that he’d catch him with only a few laps remaining.
On lap 40 of 44 Hamilton got within a second of his teammate, but in the same machinery he struggled to find a meaningful advantage with which to launch a move.
It allowed a perfectly defensive Russell to close the deal, taking the chequered flag by 0.526 seconds.
“Amazing result,” Russell gushed. “We definitely didn’t predict this win this morning in our strategy meeting, but the car was feeling really awesome.
“Well done to Lewis, because he really controlled that race, and of circumstances were slightly different, I’m sure he would have got the victory.”
But Russell’s celebrations were cut short with a report from the technical delegate that his car had weighed in below the mandatory 798-kilogram minimum, attracting automatic disqualification from the stewards.
Mercedes accepted it had been a “genuine error” without mitigating circumstances.
The car’s minimum weight includes tyres. The team theorised that Russell’s unplanned 34-lap stint on one set of tyres meant the rubber had worn down more than calculated, leaving him below the limit.
A quirk of the long Spa-Francorchamps lap also means drivers don’t complete a cool-down lap, meaning they’re unable to pick up discarded rubber and other detritus on their tyres on the way back to pit lane to bolster car weight.
Hamilton inherited the victory, his second of the season and Mercedes’s third from the last four grands prix, but the Briton said the outcome was bittersweet.
“Mixed feelings for today’s result,” he wrote on social media. “Obviously happy to get the win, but I feel for George, and it’s disappointing for the team not to get the one-two.
“A lot of positives to take from today, though. At the start of the weekend we didn’t expect to be at the front or the pace we had, so it’s great to see just how much progress has been made and that we are in the fight.”
Oscar Piastri moved up to second, extending McLaren’s podium streak to 10 successive grands prix, closing the team’s deficit to Red Bull Racing in the constructors championship to 42 points with 10 rounds remaining.
Pole-getter Leclerc moved up to third, the Ferrari driver lamenting that he didn’t have the pace to run with the leaders.
Max Verstappen recovered from 11th to fourth in a Red Bull Racing car that clearly no longer has a competitive edge even at one of its historically strongest circuits, the Dutchman ruing the performance penalty for running in dirty air that slowed his progress.
Lando Norris came off second-best to a race-long battle with Verstappen, leaving him fifth ahead of Carlos Sainz.
Sergio Pérez finished seventh, a distant last among the frontrunners, in a lacklustre performance from the front row of the grid that has ramped up pressure on the Mexican, whose future with the team beyond the August break is up for discussion by management this week.
Fernando Alonso was the only other driver to successfully make the finish on one stop, leading the midfield in eighth ahead of Esteban Ocon and Daniel Ricciardo in the final points-paying places.