Armstrong used his right foot to steady himself, and was able to stay on the bike.
His teammates, wearing special shirts with a band of yellow on right shoulder, recovered and led him up the Champs-Elysees at the front of the pack.
Organizers then announced that they had stopped the clock because of the slippery conditions with more than 10 miles to go.
Vinokourov surged ahead of the main pack to win the last stage. He had been touted as one of Armstrong's main rivals at the start of the Tour on July 2, but like others was overwhelmed by him.
Armstrong's departure begins a new era for the 102-year-old Tour, with no clear successor. His riding and his inspiring defeat of cancer attracted new fans - especially in the United States - to the race, as much a part of French summers as sun cream, forest fires and traffic jams down to the Cote d'Azur.
Millions turned out each year, cheering, picnicking and sipping wine by the side of the road, to watch him flash past in the race leader's yellow jersey, the famed "maillot jaune."
Cancer survivors, autograph hunters and enamored admirers pushed, shove, and yelled "Lance! Lance!" outside his bus in the mornings for a smile, a signature, or a word from the champion.
He had bodyguards to keep the crowds at bay - ruffling feathers of cycling purists who sniffed at his "American" ways.
Some spectators would shout obscenities or "dope!" - doper. To some, his comeback from cancer and his uphill bursts of speed that left rivals gasping in the Alps and Pyrenees were too good to be true.
Armstrong insisted that he simply trained, worked and prepared harder than anyone. He was drug-tested hundreds of times, in and out of competition, but never found to have committed any infractions.
Armstrong came into this Tour saying he had a dual objective - winning the race and the hearts of French fans. He was more relaxed, forthcoming and talkative than last year, when the pressure to be the first six-time winner was on.
Some fans hung the Stars and Stripes on barriers that lined the Champs-Elysees on Sunday. Around France, some also urged Armstrong to go for an eighth win next year- holding up placards and daubing their appeals in paint on the road.
Armstrong, however, wanted to go out on top - and not let advancing age get the better of him.
"At some point you turn 34, or you turn 35, the others make a big step up, and when your age catches up, you take a big step down," he said Saturday after he won the final time trial. "So next could be the year if I continued that I lose that five minutes. We are never going to know."Javier Soriano/AFP/Getty Images The peloton cruises down the rain-soaked roads of the Champs Elysees in Paris.
Top 10 results, Stage 21: a 144.5km ride from Corbeil-Essonnes to Paris
1. Alexander Vinokourov (KAZ/MOB) 3h40min 57sec
2. Bradley McGee (AUS/FDJ) at 0:00
3. Fabian Cancellara (SWI/FAS) 0:00
4. Robbie McEwen (AUS/DAV) 0:00
5. Stuart O'Grady (AUS/COF) 0:00
6. Allan Davis (AUS/LTY) 0:00
7. Thor Hushovd (NOR/C.A) 0:00
8. Baden Cooke (AUS/FDJ) 0:00
9. Bernhard Eisel (AUT/FDJ) 0:00
10. Robert Forster (GER/GRL) 0:00
Stage 21: Complete results
Top 10, Final Overall standings 1. Lance Armstrong (USA/DIS) 86h15min 02sec
2. Ivan Basso (ITA/CSC) at 4:40
3. Jan Ullrich (GER/MOB) 6:21
4. Francisco Mancebo (SPA/BAL) 9:59
5. Alexander Vinokourov (KAZ/MOB) 11:01
6. Levi Leipheimer (USA/GRL) 11:21
7. Michael Rasmussen (DEN/RAB) 11:33
8. Cadel Evans (AUS/DAV) 11:55
9. Floyd Landis (USA/PHO) 12:44
10. Oscar Pereiro (SPA/PHO) 16:04
Stage 21: Complete overall standings
Stage 21: Category standings