* Gasly takes first win in Monza thriller
* Sainz second for McLaren, Stroll third
* Hamilton goes from first to last to seventh
* Briton retains 47-point lead
(Note vulgar language in 17th paragraph)
By Alan Baldwin
Sept 6 (Reuters) - France's Pierre Gasly took a shock Italian Grand Prix win for Italy-based AlphaTauri on Sunday in a race packed with suspense and surprises after Formula One's top teams made mistakes or failed to finish.
McLaren's Spaniard Carlos Sainz chased Gasly across the line at a spectator-free Monza deprived of its usual atmosphere by the COVID-19 pandemic, with Racing Point's Lance Stroll completing a youthful podium.
Mercedes's championship leader Lewis Hamilton finished seventh after starting on pole, leading and dropping to last following a 10-second stop/go penalty for entering the pit lane under a red light during the first of two safety car deployments.
Despite the setback, the six-times world champion fought back and retained his 47-point lead at the top -- now over team mate Valtteri Bottas, who made a dismal start and was fifth.
Hamilton, who equalled a Formula One record with his 41st successive classified finish and took a bonus point for fastest lap, has 164 points after eight races to Bottas's 117.
Red Bull's Max Verstappen, previously Hamilton's closest rival, retired with mechanical problems and dropped to third on 110 points.
It was the first time since 2013, when Kimi Raikkonen triumphed with Lotus in Australia, that a team other than Mercedes, Ferrari (NYSE:RACE) or Red Bull had won a race.
"It's unbelievable," gasped Gasly, who was demoted by Red Bull's main team last year in a switch with Alexander Albon but has come on in strides in a season disrupted by COVID-19 and without spectators.
"It was such a crazy race and we capitalised on it. I've been through so much in 18 months, I struggle to realise this," added the 24-year-old of his first F1 win.
FIRST SINCE PANIS
The victory was also the first by a French driver since Olivier Panis in 1996 and the second for the former Toro Rosso team whose only other win was also at Monza with Sebastian Vettel in 2008.
"I was so close but yet so far," said Sainz, who had also dreamed of taking his first win before joining Ferrari next year. "I needed one more lap."
The race had to be stopped at the halfway mark, 27 laps, after Ferrari's Charles Leclerc crashed heavily into the tyre wall at Parabolica, emerging unscathed from the impact but still taking a trip to the medical centre.
The earlier safety car period was caused by the Ferrari-powered Haas of Kevin Magnussen stopping by the side of the track.
Leclerc's team mate Vettel had already retired with brake failure on his final Italian GP with Ferrari, crashing through polystyrene marker boards, and the chances of hearing the Italian anthem on the podium had appeared to be nil.
Hamilton used the long stoppage to scoot off and see the stewards -- who showed him evidence he could not dispute.
The Briton went from first to last in the space of a lap after the standing restart, with Gasly taking the lead when Hamilton took his penalty.
"That's some bullshit," Hamilton said over the radio of a situation that left him 30 seconds off the lead in a 17-car field that offered a glimpse of what a reverse-grid sprint race might look like.
He still managed to lap faster than the rest, reeling in rivals before running out of time.
Lando Norris was fourth in the other McLaren, with Australian Daniel Ricciardo sixth for Renault (PA:RENA) and team mate Esteban Ocon eighth.
Gasly's Russian team mate Daniil Kvyat was ninth and Stroll's Mexican team mate Sergio Perez 10th.
The race also marked a farewell for the Williams (NYSE:WMB) family after the sale of the team to U.S.-based Dorilton Capital. Canadian Nicholas Latifi came close to their first point of the year in 11th.