Bradley Wiggins finished in 21st place on his competitive rowing debut at the British Indoor Championships in London.
Wiggins, who retired from cycling in December 2016 as a five-time Olympic champion, was competing in the elite men's 2,000m race.
He began slowly after mistakenly believing he had false started, before finishing in six minutes 22.5 seconds, while Adam Neill won in 5:48.2
Wiggins later referred to the incident as a "schoolboy error".
"Upon hearing a call in the background, I thought the race had false started," the 37-year-old wrote on Twitter.
"Fantastic experience racing with everyone, I will come back 12 months stronger next year."
Wiggins first raised the possibility of changing sports in 2012, before announcing his intention to race in London last month.
The British Rowing Indoor Championships are open to anyone, and competitors from across the UK range from 11 to 88 years of age.
Two-time Olympic rowing champion James Cracknell, who is mentoring Wiggins, said he expected him to come back stronger.
"Bradley knows how to race. His rhythm looked very good. He doesn't want to go out on failing and he will want to come back and do it better," Cracknell said.
Race winner Neill also praised Wiggins, saying he has a way to go "but his improvement curve will be high".
"When he sets his mind to something he doesn't let things get in his way. He still has to learn about rowing on the water, but I don't see any reason he can't give it a go," Neill added.