AP Sports Writer

MONTE PETRANO, Italy (AP) Lance Armstrong's preparation for the Tour de France is going so well, the seven-time Tour winner put aside his own ambitions to help a struggling teammate.

On a day when the thermometer soared to 100 degrees, Armstrong was riding with the race favorites up the final climb of the 16th stage of the Giro d'Italia on Monday when he realized that fellow Astana rider Levi Leipheimer had dropped behind.

Armstrong looked over his shoulder to see where his teammate was and slowed to escort Leipheimer to the finish.

Armstrong and Leipheimer finished 2 minutes, 51 seconds behind stage winner Carlos Sastre. Denis Menchov crossed second, 25 seconds after Sastre, and retained the overall leader's pink jersey.

"I would have lost much, much more time. He saved me minutes and minutes," Leipheimer said of Armstrong's help. "You see the difference between a seven-time Tour winner like Lance. He was stronger and had to wait for me today. I just didn't feel like I had it today."

Still, Leipheimer dropped from third to sixth overall, 3:21 behind Menchov.

"I was not as strong as those guys, it's plain and simple," said Leipheimer, who has been riding with several cuts and bruises since a crash last week. "It was hot for everyone. Today was the day that separated everyone and you see who's strong and who's not."

Sastre, the defending Tour de France champion from Spain, clocked a marathon-like 7 hours, 11 minutes, 54 seconds over the lengthy 147-mile leg from Pergola to Monte Petrano, over three major climbs.

"I knew I had a chance to do something today and I did," Sastre said. "This was the toughest stage of this year's Giro."

Sastre also won the most difficult stage in last year's Tour, at Alpe d'Huez.

Danilo Di Luca crossed third, 26 seconds after Sastre, and Menchov increased his lead over Di Luca to 39 seconds. Sastre moved into third overall, 2:19 back.

Armstrong moved up from 13th to 12th overall, 11:06 behind Menchov. The Texan is still regaining his form after 3 years of retirement and then breaking his collarbone in March.

"He's looking very good after three years off the bike and a big accident one month before the Giro," Menchov said. "He's going to come out of this Giro very strong and he's going to put on a big show in the Tour."

When they crossed the finish line, Armstrong appeared much fresher than Leipheimer and he put his hand on Leipheimer's shoulder and said, "Sorry man."

Armstrong has stopped speaking to reporters, but on his Twitter feed he called it "one of the hardest" stages he's ever seen.

"Relentless climbing and oppressive heat. Levi had a day tough (day), but we tried to limit his losses," Armstrong wrote. "Hot days like this are always full of surprises."

Another Astana rider, Yaroslav Popovych, was part of an early breakaway and was the last man caught by Sastre.

"They told me on the radio that Sastre was coming really fast, chasing me. I didn't want to believe it," Popovych said. "When he finally passed me I lost all my strength. What a day, I stayed in the breakaway for 240 kilometers (150 miles)."

Sastre caught Popovych with 1.6 miles to go, and the Ukrainian finished 18th, 3:21 behind.

"I think the strongest guy won today, no doubt about that, so no regrets," Astana team manager Johan Bruyneel said. "On the other hand, Levi did not have the legs on the last climb, so we tried to limit the damages. It was good to see how Lance helped Levi all the way to the finish. It was great teamwork.

"It's not possible to win the Giro anymore but we'll still try to get Levi on the podium in Rome. Maybe he just had a bad day."

After a rest day Tuesday, the race resumes Wednesday with another uphill finish in a short 52-mile stage from Chieti to Blockhaus.

The race ends Sunday with a short individual time trial in Rome.

Copyright 2009 The Associated Press.