By Piers Newbery
BBC Sport at Wimbledon
Williams struggled with Cavaday's serve in the early stages
Venus Williams opened her Wimbledon title defence with a 7-6 (7-5) 6-1 win over Naomi Cavaday, despite a spirited display from the Briton.
The American, 28, inexplicably dropped her opening service game from 40-0 and Cavaday soon moved into a 3-1 lead.
Four-time champion Williams levelled in game six but still needed a tie-break before racing through the second set.
She goes on to face another Briton, Anne Keothavong, who saw off Vania King 4-6 6-2 6-3.
The defending champion's opening match on Centre Court should have been straightforward according to the rankings, with Cavaday 190 places lower at 197 in the world.
But Cavaday's powerful hitting from the baseline and swinging left-handed serve appeared to catch Williams off guard in the early stages.
After throwing away her first service game, the American broke back for 3-3 but could not put Cavaday away.
Venus 'always looking to improve'
It was a similar story in the tie-break, with Williams finally edging it when Cavaday netted a backhand, and the American took control with a break early in the second set.
"She played excellent and really took advantage of her opportunities," said Williams afterwards.
"She played with poise on Centre Court in front of her home crowd. She served well, really returned the ball with force and ran a lot of balls down - I was impressed with her game."
Cavaday felt she did herself justice after being handed a wildcard for the tournament.
"It was a great experience," the 19-year-old from Kent said. "I was pretty nervous before I went out but as soon as I did I felt I belonged there.
"I was relaxed, ready and raring to go. I was looking forward to this match as soon as I heard the draw - I worked hard in the build-up and I hope I showed it.
A lot of what happened in the first set was down to her play and not me but I wasn't really concerned - I felt pretty comfortable
"I wanted to fight and compete - I love getting stuck into matches and I got off to a great start.
"I went at her and gave everything I had got. I took the lead in the first game and I felt I was matching her shot for shot."
Cavaday's only regret was that she let the second set slip away without more of a fight after being edged out of the opener.
"I really enjoyed myself," she explained. "It was just a shame she edged me to the first set - I think she relaxed more after that.
"The second set got away from me - I wasn't tired but I am disappointed that I didn't make enough first serves to give myself a chance."
Williams admitted to being surprised by how hard she was pushed in the early stages but was happy to be given such a stern test.
"A lot of what happened in the first set was down to her play and not me but I wasn't really concerned - I felt pretty comfortable," she explained.
"I had a few chances to break but it didn't quite happen so I had to leave it behind me and go for the tie-break.
"In the second set the difference was my returns were a little better but I always feel like I play better as the match progresses.
"I felt my level of play was good and it is nice to have a really challenging opponent early on."