Armstrong said he had to overcome pre-race nerves on his comeback
Lance Armstrong finished 64th as an estimated crowd of more than 130,000 watched his comeback on Sunday.
Competing in the prologue to the Tour Down Under in Adelaide, the 37-year-old American admitted he had suffered from pre-race nerves.
"There was a lot of anxiety. It's good the first day is over and now I can get into the racing," he said.
The seven-time Tour de France winner ended his career in 2005 but has returned to promote cancer awareness.
His official comeback will be the tour's first stage on Tuesday as Sunday's criterium, won by Robbie McEwen, is not a sanctioned race.
"I think the last time I did that fast a race was probably back in 1990. I found it a bit safer and easier in the back," said Armstrong.
"I was a bit nervous in the corners but the hardest thing was the sun. In one or two corners you really had the sun in your eyes."
Armstrong's team manager at Astana, Johan Bruyneel, admitted it was a relief finally to see the American back racing after a three-and-a-half year break.
"It's a special day. There's been all this talk about the comeback and now it's finally a fact," said the Belgian.
"The instructions were for Lance and the whole team not to concentrate too much about the race but just to get through it. It was better to stay at the back and stay out of trouble.
"This is an important moment. He's finally a bike racer again. I could see he was really enjoying it."
The first stage of the Tour Down Under is Tuesday's 145km ride from Norwood to Mawson Lakes.