Laura Robson credited opponent Serena Williams after crashing out in the second round of the Internazionali d'Italia in Rome 6-2 6-2.
The 19-year-old Brit knocked out Serena's older sister Venus the previous day and was fast off the blocks as she broke the 15-time Grand Slam singles champion in the opening game.
That was as good as it good for Robson, though, as eight double faults helped the American wrapped up victory in an hour and 15 minutes.
"She's number one in the world for a reason," Robson told the WTA Tour website afterwards. "She played really well. She didn't give me many opportunities.
"I thought it could have been a little bit closer - I had some break points I didn't take advantage of - but it was a learning experience and hopefully I'll play against her again soon."
Williams added: "It was a good match - she played really well and really smart. She's just a great player and I think she has such a big future.
"I've played lots of matches, but I'm the kind of player who likes to keep playing matches, at least now in my career. I just want to keep the confidence there."