Lance Armstrong took the overall leader's yellow jersey on the Tour de France after his Discovery Channel team won the stage four team time-trial.
The CSC team finished two seconds behind after yellow jersey wearer David Zabriskie fell in the last 2km.
Zabriskie trailed in behind the rest of his team and is now more than a minute adrift of six-time champion Armstrong.
Another American George Hincapie is second in the overall standings, 55 seconds behind his team-mate.
CSC looked to be on target for the stage win on the 67.5km stage from Tours to Blois before Zabriskie's tumble.
The American's team were two seconds ahead of Discovery Channel after 61.5km but Zabriskie fell in the middle of the pack causing CSC to lose precious seconds.
Zabriskie is to continue in the Tour after a medical check revealed he was not seriously injured.
He needed stitches in a cut to his right arm and hurt his knee.
CSC team media officer Brian Nygaard said: "We have just got
the results of the X-rays and nothing is broken.
"He's still got some pain in his right knee which we'll look at tomorrow (Wednesday) but he will start the stage."
Zabriskie said: "I am not happy with what happened but that's life."
Armstrong suggested the sheer physical effort needed to ride the stage could have played a part in Zabriskie's downfall.
"Team time trials are so hard that at the end of it you are at your limit and everybody is cross-eyed," he said.
"There were a lot of turns in the final kilometres and it's easy to make a mistake like that."
Jan Ullrich and his T-Mobile team took third, 35 seconds behind Discovery Channel, while Liberty Seguros took a surprise fourth.
Phonak were one minute and 31 seconds off the pace in fifth.
Stage four team-time-trial result:
1. Discovery Channel 1hr 10mins 39secs
2. Team CSC +2secs
3. T-Mobile +35
4. Liberty Seguros +53
5. Phonak +1:31
6. Credit Agricole +1:41
7. Illes Balears +2:05
7. Gerolsteiner +2:05
9. Fassa Bortolo +2:19
10. Liquigas +2:26
11. Davitamon - Lotto +2:32
12. Rabobank +2:48
13. Domina Vacanze +3:04
14. Quick-Step +3:05
15. Bouygues Telecom +3:08
16. Euskaltel +3:59
17. Lampre - Caffita +4:09
18. Cofidis +4:28
19. Francaise des Jeux +4:46
20. Saunier Duval +5:06
21. AG2R +5:23
1. Lance Armstrong (US/Discovery Channel) 9hrs 59mins 12secs
2. George Hincapie (US/Discovery Channel) +55secs
3. Jens Voigt (Ger/Team CSC) +1:04
4. Bobby Julich (US/Team CSC) +1:07
5. Jose Luis Rubiera (Spa/Discovery Channel) +1:14
6. Yaroslav Popovych (Ukr/Discovery Channel) +1:16
7. Alexandre Vinokourov (Kaz/T-Mobile) +1:21
8. Benjamin Noval (Spa/Discovery Channel) +1:26
9. David Zabriskie (US/Team CSC)
10. Ivan Basso (Ita/Team CSC)