Heather Watson let an opportunity to match her best showing at Wimbledon slip from her grasp.
The British No.2 made an impressive start against 20th seed Anett Kontaveit, but faded badly and bowed out 7-5 6-1 in an hour and 14 minutes.
Watson matched Kontaveit throughout a tight first set, only for the Estonian to snatch it with a late break of serve.
The 27-year-old, playing at her 10th Championships, capitalised on an edgy start from Kontaveit to break serve in the first game.
At 2-0, Watson was finding her range with some powerful winners to raise hopes of becoming the first Brit through to round three.
However, that was as good as it got. The pair went on to share three breaks of serve between them and the set was level at 5-5 when Watson blinked first.
The wheels promptly came off as Kontaveit began to pull away with a double break, and she found the line at the end of a long rally to finish Watson off.
"I thought in general I was too defensive. I didn't use my variety enough, coming to the net," said Watson, who has reached the third round three times.
"I think I came to the net like twice. I think I won both points. Usually in my game, I like to hit drop-shots. I'm not like a power baseliner. I use my variety to help me win these matches. But I let her dictate play.
"That first set, I just felt like I had so many chances but wasn't able to play aggressive tennis and get there. I sort of went on the back foot and just made too many errors.
"After that first set, I don't feel that I changed a lot. I just feel like she relaxed and really stepped up her level, and didn't give me a look in at all."
Former World No.1 Victoria Azarenka dropped just two games in sweeping aside Ajla Tomljanovic.
Azarenka, who reached the Wimbledon mixed doubles final with Jamie Murray last year, joked that she was disappointed to be overlooked by Andy this time around.
Asked why she was not playing that format this year, she said: "Well, Andy Murray didn't ask me to play (smiling). I'm kind of p***** about that (smiling). Actually, no, that's okay. I was hoping with the success that I had with Jamie last year I was going to be honoured to get asked, but whatever (smiling).
"No, I mean, last year was fun, because for me, at that time of my career, it was important to get just any matches: singles, doubles, mixed doubles. It was important to be on the court and to get the practice and to have that competitive spirit and be competitive again, to get opportunities.
"So it was definitely good for me to play as many matches. I don't know how much it helped me to play this year in terms of grass-court tennis, but it definitely helped me a lot at that stage of my career."