Ralf Schumacher felt Mercedes lacked pace at the US GP, claiming the W12 was “tiny bit powerless” at times.
Lewis Hamilton had to settle for second place in a race when almost everyone expected him to easily win.
Despite losing pole position to Max Verstappen on Saturday, the Briton fought back to take the lead on the first lap of the race and quickly put some distance between himself and Verstappen.
Red Bull replied by placing the Dutchman on an aggressive strategy, with both pit stops trying for the undercut.
Eight laps before Hamilton pitted, the second stop happened, and the Mercedes driver quickly began to close in on the title leader with his fresher tyres.
Hamilton eventually ran out of laps, and Verstappen won by 1.333s.
“Mercedes couldn’t keep up with the performance at the beginning,” Schumacher, a former F1 driver.
“By the time Lewis got the speed, the race was over.
“The Mercedes was a bit powerless at times.”
Verstappen’s eighth win of the season has put him 12 points ahead of Hamilton in the World Championship race.
If Mercedes were to continue their seven-year reign at the top of the standings, Schumacher believes they must find something unique.
“Red Bull has taken a step forward,” he said. “Mercedes has to stretch. Red Bull is slightly ahead. It remains exciting.”
Toto Wolff, on the other hand, believes Red Bull chose the undercut “out of necessity” since Hamilton was “awesome” on the day.
“You could see the different strategies [between the teams],” said the Mercedes motorsport boss.
“One went for the undercut out of necessity and it was a very courageous move, because it was very early, and then the second time again [they pitted first] to their advantage.
“Max’s driving, particularly in the last stint, you saw that he had learned from the first stint not to damage the tyres too early.
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