Bourg-Saint-Maurice, France ? Lance Armstrong mustered one of his strongest showings yet at this Tour de France on Tuesday, a dazzling burst of acceleration from yesteryear that allowed him to keep second place.

The seven-time champion was so buoyed by the performance that he suggested to The Associated Press he could still contend for the yellow jersey if teammate and race leader Alberto Contador has a “bad day.”

Armstrong, speaking after the 16th stage in the Alps, stressed he doesn’t expect that to happen and only a “big shake-up” would allow for such a scenario.

Contador, the 2007 Tour winner, had to fight to retain the overall lead in the 99-mile stage from the Swiss town of Martigny to Bourg-Saint-Maurice, France, which was won by Mikel Astarloza of Spain.

As Contador tried to keep pace with two attackers on the final climb, the 37-year-old Texan lagged. But after dropping back at least 35 seconds, he popped out of his saddle and recovered lost ground.

“I had no choice. … So I waited until we had a steeper section and then I got away with an acceleration,” he said.

Contador was impressed, but not surprised.

“It’s easy to explain — he’s a very great rider,” said Contador, who leads his Astana teammate by 1:37. “He was in the past, and he showed it once again.”

Contador and Armstrong finished in a small group of race leaders behind Astarloza. The route featured the highest peak this year, the snowcapped Grand-Saint-Bernard pass on the Swiss-Italian border, at 8,113 feet, and its sister the Petit-Saint-Bernard pass, on the Italian-French border.

Armstrong says he’s feeling better on his bike than he did during Sunday’s entree into the Alps, when Contador dusted him and the entire pack on the ride up to the Swiss ski station of Verbier.

“I made some changes to my position yesterday — I raised the seat height,” he said. “So in general, I was pedaling better today.”

Armstrong, back at the Tour after 3 1/2 years of retirement, committed himself to help Contador win the three-week race after the Spaniard took the yellow jersey that day. Armstrong appeared to shut down his own ambitions then. But at cycling’s main event — which ends Sunday in Paris — anything can happen.

“If there was a massive shake-up and something happened, then I’d have to be strong — to represent the interests of the team,” Armstrong said. “But I don’t think that’s going to happen.”

“If he were to have a bad day, I think I could cover the moves for the team,” he added. “But I don’t think he’s going to have a bad day.”

In the interview, Armstrong was coy about competing next year, saying only: “There’s a pretty good chance I’ll be there.”

But in an e-mail to the AP later in the day, Armstrong’s manager Mark Higgins said the Texan will “for sure” be part of the race next year.

Asked whether he plans to announce a new team, as has been widely speculated, Armstrong told the AP: “Come on, man, you’re killing me … let’s talk about music or something.”

On his Twitter account Tuesday, he wrote that his team has a new American sponsor for next year, but he wouldn’t provide details until Thursday.

Armstrong already has shown his guile and guts at this Tour. He eclipsed Contador in the standings in Stage 3, by cleverly catching a ride in a wind-swept lead group. In the opening day time trial, he was 10th — 40 seconds behind Swiss winner Fabian Cancellara — and only 22 seconds slower than Contador.

But the Spaniard clearly has been the strongest man in the mountains. He outpaced Armstrong in both uphill finishes this year — in Andorra, in the seventh stage, and in Verbier.

Contador had a struggle on his hands in fending off brothers Andy and Frank Schleck of Luxembourg on the Petit-Saint-Bernard, the second of the day’s climbs.

“I gave my maximum, ” he said. “I could resist but not without difficulty. I’m happy after this difficult day.”

Astarloza, who rides for the Euskadi Euskaltel team, thrust his fists in the air and kissed his fingers as he crossed the line in 4 hours, 14 minutes, 20 seconds. He was six seconds ahead of French riders Sandy Casar and Pierrick Fedrigo.

With a little more than a mile to go, the Spaniard escaped three other breakaway riders with him and held on for his first stage win on the Tour.

“This is the biggest day of my career,” Astarloza said.