LONDON (AP) — After advancing in the men's doubles at Wimbledon on Thursday, Jack Sock finally discussed his opening-round singles defeat and the fine that followed.

On Tuesday, having earned a two-set lead against 81st-ranked Matteo Berrettini of Italy, Sock fell to a 6-7 (5), 6-7 (3), 6-4, 7-5, 6-2 loss.

As they shook hands at the net, 18th-seeded Sock used an obscenity to tell Berrettini what he thought of the winner's coach.

Sock was fined $5,000 for unsportsmanlike conduct. He left the grounds Tuesday without speaking to the media, but sat down with a small group of reporters Thursday and explained that he thought Berrettini's coach was "talking down" to him throughout the match.

"He was in the wrong for saying the things he did," Sock said. "I'm definitely in the wrong for saying what I did after the match. I shouldn't have gone that far."

The American — who won the Wimbledon doubles title with Canadian Vasek Pospisil in 2014 — has teamed up this year with three-time champion Mike Bryan, whose brother and usual partner Bob is recovering from a hip injury.

The pair were ahead and moved into the second round when their opponents —Daniele Bracciali and Andreas Seppi — stopped in the second set.

Despite his success in doubles, Sock said he wants to focus on singles.

After reaching a career-high No. 8 in the rankings in November and qualifying for the season-ending 2017 ATP finals, Sock has struggled this year.

Despite having lost six matches in a row and seen his record fall to 5-13 for the season, the 25-year-old remains confident of turning things around.

"In tennis that's the beauty," Sock said. "You can always suit up the next week and play another tournament and always have the chance to win it."

The American is taking a similar attitude toward criticism of his behavior.

"I'm not going to sweat it too much," Sock said. "I know the person I am."