Norway's Thor Hushovd wins the prologue in eight minutes 17.00 seconds with the USA's George Hincapie 0.73secs adrift.
Another American, last year's prologue winner David Zabriskie, finishes 3rd, with overall favourite Alejandro Valverde four seconds adrift in 5th.
Quadruple British Olympic medallist Bradley Wiggins, making his Tour debut, finished 14 seconds behind in 16th.
Scot David Millar, returning to competition after serving a two-year doping ban, was a second back in 17th.
1 Thor Hushovd (Nor) 8:17.00
2 George Hincapie (USA) 8:17.74
3 D Zabriskie (USA) 8:21.21
4 Sebastian Lang (Ger) 8:21.80
5 Alejandro Valverde (Spa) 8:21.93
LATEST UPDATES (all times BST):
1515: Last year's prologue winner, David Zabriskie, finishes four seconds adrift of Hushovd, before the last man out on the course, George Hincapie comes agonisingly close before settling for second, 0.73 seconds behind the Norwegian.
1510: Spaniard Alejandro Valverde makes a promising start to to his Tour bid as he comes home in 8:21.93 to move into third place.
1506: Norwegian Thor Hushovd smashes the fastest time to finish in 8.17.01, taking over the lead from Lang.
1504: David Millar's dream of returning to the Tour in the yellow jersey is dashed as he comes home in 8:31.66, currently in seventh place.
1502: American Floyd Landis, second favourite overall according to the bookmakers, is also on the course.
1500: Spaniard Alejandro Valverde, the new Tour favourites but not renown for his time-trialling, starts his challenge for the yellow jersey.
1458: Overall contender Paolo Savoldelli comes home strongly in 8:25.03 to move into third place.
1457: Quadruple Olympic medallist Bradley Wiggins is also on the course, starting a minute behind Millar.
1456: Scot David Millar, making his return after a two-year ban for doping, pushes down off the start ramp to begin his prologue.
1449: Italian Paolo Savoldelli of the Discovery Channel team, winner of the 2005 Giro d'Italia and considered an overall contender, pushes his way onto the course.
1443: Veteran Italian Gilberto Simoni, not a renown time-trialler, comes home 34 seconds behind Sebastian Lang.
1435: Britons David Millar and Bradley Wiggins will be out on the course in around 20 minutes, with Millar due to start at 1456 and Wiggins at 1457.
1430: McEwen, one of the Tour's leading sprinters, comes home in 8:45.33, 24 seconds adrift of the leader.
1425: Robbie McEwen, three times winner of the Green Jersey, is out on the course, as is Germany's Jens Voigt of Team CSC.
1417: America's Bobby Julich comes home in 16th place, 14 seconds behind the leaders.
1402: Posthuma loses his early speed and comes in 11th, 12 seconds adrift. Ukrainian Yaroslav Popovych, one of the overall contenders, finishes 15 seconds adrift of leader Lang.
1355: Dutchman Joost Posthuma sets a new best at the intermediate checkpoint of 04:06, a second better than O'Grady.
1350: Ekimov comes home in 8:34.58, seventh of the first 86 riders to finish. Fellow Russian Vladimir Karpets and Ukrainian Serhiy Honchar become the third and fourth riders to finish inside 8:30.
1345: Russian Viacheslav Ekimov, starting his 15th Tour de France, one less than the record-holder, Dutchman Joop Zoetemlek, is on the course and is fifth at the intermediate checkpoint, three seconds adrift of O'Grady.
1340: O'Grady cannot quite maintain his speed right to the end, finishing 13 hundredths of a second behind Lang in 8:21.93. 76 riders have now completed the course.
1335: Australian Stuart O'Grady, riding for Team CSC, sets a new quickest time at the 3.7km checkpoint of four minutes, seven seconds, a second quicker than the current leader Sebastian Lang.
1325: The best-placed finisher from last year's Tour left in the field - American Levi Leipheimer, who finished sixth - will start his prologue at 1506 BST.
1315: German Sebastian Lang, of the Gerolsteiner team, takes 10 seconds off the time of compatriot Bert Grabsch to set a new target of 8:21.80.
1310: The last man to go off in the prologue will be American George Hincapie, the new leader of the Discovery Channel team following Lance Armstrong's retirement.
1300: The riders are going off a minute apart, with around a quarter of the 176 having started or completed the course. Only two of the 44 finishers so far have come in inside 8:40.
1255: American Christopher Horner comes closest to beating Grabsch's early target, but finishes narrowly outside with 8:32.61, a second adrift.
1245: Frenchman Laurent Brochard clocks 8:40.99 to move into second place, but Grabsch still leads with 24 riders having completed the course.
1240: With 176 riders in all, 13 of the original 189 entries having withdrawn amid a doping investigation, the leading candidates will not start for a couple of hours yet, but of the first 15 to finish, German Bert Grabsch sets the early pace with 8:31.89.
1235: Italian Fabio Sacchi, riding for Team Milram, sets the early target time after completing the 7.1km course in eight minutes, 51.93 seconds.
1225: German Bert Grabsch, of the Phonak team, is the quickest of the early riders at the first intermediate point at 3.7km, the Quai des Belges, which he reaches in four minutes, 14 seconds.
1215: Frenchman Cedric Coutouly is the first rider to set off on the 7.1km course around Strasbourg.
The Tour starts without the top five riders from last year's race, following the retirement of seven-time winner Lance Armstrong and a doping investigation claiming, either directly or indirectly, the other four.
Pre-race favourites Ivan Basso and Jan Ullrich (second and third last year) were two of 13 riders withdrawn by their teams, as was Spain's Francisco Mancebo, fourth last year.
Kazakh Alexander Vinokourov, fifth last year, is unable to compete after his Astana-Wurth team withdrew en masse after five team-mates were on the investigation's list.