Martin wins crash-filled sprint at Spanish MotoGP
Teenager Pedro Acosta was runner up to take second in the championship race with former world champion Fabio Quartararo third as nine riders failed to finish.
All three podium finishers described the track, dappled with damp after morning rain, as tricky.
"A difficult race, the track conditions were super hard," said Martin in his on-track interview.
Marquez, with his first pole since joining Ducati Gresini, and Martin started on the front row, but South African Brad Binder shot off from the second row to grab the lead on his KTM.
Spaniard Martin, on a Ducati-Pramac, overtook on lap two and pulled away from the chaotic battle behind him as riders kept tumbling.
Two-time defending champion Francesco Bagnaia went down on lap three. Binder squeezed past on the inside, forcing the Italian into another bike. Bagnaia's Ducati went flying, out of the race and out of the points.
Martin built a comfortable lead but Marquez was the fastest bike on the course and closed in. Under pressure, Martin made a mistake on lap seven and Marquez pounced.
With three laps left Marquez hit a damp patch and slid off. He remounted to finish seventh.
"I had a good start but then I saw Marquez was coming even though I was pushing a lot, a lot, a lot," said Martin.
'Did not matter'
"Marc overtook me because I made a mistake on corner seven. Then I tried to push him and he made a mistake."
Acosta, who started on the fourth row on his GasGas, came through to take second.
Martin went to 92 points in the standings, 29 clear of Acosta who took over second, four points head of Italian Enea Bastianini of Ducati who did not finish.
Spaniard Maverick Vinales, a double winner in Austin last time, is fourth after he too fell on his Aprilia.
Acosta, who appeared surprised when told he was second overall, said it "did not matter".
"We know we have the pace, but it was quite tough starting from 10th after the crash in qualifying," said the 19-year-old.
"With the mixed conditions it was not easy. The wet patches were quite wet and it was easy to lose the rear tyre. It happened that I touched a wet patch and went wide."
Yamaha's Quartararo, who had started 23rd out of 25 riders, held off a late challenge from Spanish veteran Dani Pedrosa on a KTM to complete the podium.
"Starting from P23 it was a great race," said Quartararo, world champion in 2021.
"The track was really tricky. Of course, a lot of crashes in front but I managed to get the first podium of the year on the sprint."
Martin said he hoped the track would be easier for Sunday's main race.
"Tomorrow in dry conditions it will be a different story," he said.