Beaten Keys earns Radwanska praise, Stephens splutters LONDON (Reuters) - Madison Keys lost at Wimbledon on Saturday after fellow American Sloane Stephens came through her third round match but it was the teenager who got the plaudits after nearly upsetting last year's runner-up Agnieszka Radwanska. Poland's Radwanska survived, winning 7‑5 4‑6 6‑3, but Keys lived up to her billing as the American most likely to challenge for major honors when 16-times grand slam champion Serena Williams decides to hand over the baton. Stephens, the 17th seed, survived to reach the last 16 at Wimbledon for the first time but she put in a patchy performance against 196th-ranked Petra Cetkovska to whom she lost eight games in a row before pulling off a 7-6 (3) 0-6 6-4 victory. Keys, 18, boasts a serve that former American great Chris Evert believes can turn into a weapon like that owned by world number one Williams, while she also has the heavy groundstrokes to back it up from the baseline. Keys cracked down 15 aces against fourth seed Radwanska, with her first serve almost breaking the 120mph-barrier at times. Her total winner count was 67, compared to Radwanska's 23, although the unforced errors also piled up. Radwanska was clearly impressed with what she saw. "She was really playing great tennis," Radwanska, who beat Keys 6-1 6-1 in Miami this year, told reporters. Especially she was serving unbelievable. Even when I had some break points a couple of times I couldn't do anything. I think a couple of months ago some journalist asked me who is one of the young players coming up. I picked her. She can really do well. If she's going to work and play like this, we're going to see her much more often. Keys showed plenty of guts too, saving three match points at 3-5 in the decider, two of them with booming aces. "I just thought, 'Hit the biggest serve you possibly can'," Florida-based Keys, who made her WTA Tour debut aged 14, told reporters. I was kind of impressed with my serving today. Keys said she was just happy to be part of a burgeoning group of American women players of which, including Williams, there are 10 in the top 100 of the WTA rankings. Australian Open semi-finalist Stephens is currently leading the chase but lacks the heavy-artillery of Keys. However, she proved on Saturday she has that crucial knack of pulling out victories when not playing well. Her match resumed at the start of the third set on Saturday after it had been interrupted by bad light on Friday after Stephens had lost the second set 6-0. When she went 2-0 down and a point away from 3-0 in the decider she looked listless and her game was riddled with errors but she recovered her composure to turn things around. Today was a new day. I knew I could come out and play, go for it, play a full third set," said Stephens, who will meet a familiar face in Florida-based Puerto Rican Monica Puig for a place in the quarter-finals. It did feel weird. I thought I'm only playing one set. This is like a practice set. It was a little tricky. "I just had to go out and play, play hard," added Stephens. Reporting by Martyn Herman