British No.1 Heather Watson believes she paid the penalty for too many unforced errors after she lost to America's Sloane Stephens in the second round of the French Open.

Watson started the match with a perfect record against Stephens, having won all four of the pair's previous encounters, but her opponent was too strong in Paris and eased to a 6-2 6-4 victory.

It means Watson is still to reach the third round at Roland Garros and the world number 45 admits she was disappointed with her performance.

"I think it was more me today, I think I was giving away a lot of free points," Watson said.

"I made a lot of unforced errors. Obviously she played well and did what she needed to do.

"She hit some really heavy balls which pushed me back in the beginning and kind of made me think but I think I was just very inconsistent today."

Watson had worn strapping on her right arm throughout her first round doubles defeat on Wednesday and the strapping was even heavier during her loss to Stephens.

"I've had this with my arm for a week and a bit now, but it wasn't the reason I lost today," Watson said.

"I felt fine. I had it all taped up and I took some painkillers before the match.

"It was just me really. I was just pretty sluggish and slow out there.

"Finally after like a set and a bit I finally got into it, but at that point it was kind of a little bit too late."

The match got off to the worst possible start for Watson as Stephens broke her first two service games and held her own to take a 3-0 lead.

Watson made a better fist of her fourth service game and pulled it back to 5-2, but it was not enough as the world number 40 sealed the first set.

The Briton again dropped her first service game in the second set to give the upper hand to Stephens, who secured her passage into the third round in one hour and 10 minutes.

"I'm starting to play more aggressively and I'm actually starting to have more up and down results, which maybe is a good thing," Watson added.

"I'm disappointed I lost today. I thought it was a good opportunity for me, but I wasn't able to take it."

Earlier fifth seed Caroline Wozniacki was dumped out of the competition after losing her second-round tie 6-4 7-6 (7/4) to Germany's Julia Goerges.

Wozniacki has now failed to reach round three in Roland Garros since 2012 as the Dane was out-powered by a superb Goerges performance.

Goerges, ranked 72nd in the world, has won all three meetings between the pair on clay and Wozniacki admits she has a mental block when she faces the German.

"I think especially on clay she has a way to make me feel like I'm not playing very well," Wozniacki said.

"I think there are just some players that it's a tough match-up for you no matter the rankings, and some of them are easy match-ups no matter the rankings.

"Obviously she has given me trouble in the past and she gave me trouble again today so that kind of sucks.

"I would have liked to have been through to the next round, but I'm not."

Goerges, who will now play American Irina Falconi, has never gone further than the fourth round at a grand slam but she believes her style of play is difficult to combat on clay.

"I don't play the typical women's game on clay court," Goerges said.

"I play a little bit more spin, a little bit higher over the net than some of the other girls.

"When she gets the ball in her striking zone she doesn't miss any balls, but if you give her different balls then it's tougher for her.

"It's never a guarantee you're going to win the match, you have to execute as well, and that's what I did mainly today very well."