WIMBLEDON, England -- It was 9:30 a.m., local time, about 90 minutes before first ball, and Madison Keys was already sweating, crushing the ball on the Aorangi practice courts. If it seems like she’s been doing this forever, how do you think she feels?

The 28-year-old American turned professional on her 14th birthday in February 2009, which means she’s been doing this for more than half her life. She’s carved out a nice living on the strength of that booming serve and lethal forehand.

She’s won exactly 350 matches and collected more than $16 million in prize money. Keys has reached at least the semifinals at three of the four Grand Slams but, oddly, Wimbledon is the exception.

Strange, because her big game is a natural fit on grass. After Friday’s 7-5, 6-3 victory over Viktorija Golubic, Keys was through to the third round.

She will next play unseeded Marta Kostyuk, who advanced when Paula Badosa (lingering spinal injury) retired from their match trailing 6-2, 1-0.

“I think I just, from the start, [playing on grass] just felt really natural,” Keys told reporters afterward. “I feel like on clay it kind of took a little while of figuring out what small adjustments to make in my game to make my game better on the surface versus on grass. It just has always felt really easy and natural and it just immediately clicked.”

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Underlining the value of her serve on grass, Keys won all 17 first-serve points in the first set. She converted her third set point when Golubic shanked a forehand nearly into the seats around Court 12.

Keys broke through in the sixth game, jumping on a second serve from Golubic and forcing a backhand error. Keys quickly backed it up for an insurmountable 5-2 lead.

For the match, Keys won 36 of 39 first-serve points (92 percent) and was broken only once. She finished with six aces and 28 winners, 22 more than Golubic.

Wimbledon: Scores | Draws | Order of play

Keys is 20-9 (.690) at Wimbledon and 42-13 (.764) on grass for her career -- infinitely better than her records on hard courts (172-117, .595) and clay (65-43, .602). Three of her seven Hologic WTA Tour titles have come on grass, and while she also has three on hard courts, there have been far fewer opportunities on grass.

Her best season, which brought her to a career-high of No.7, was 2016 when she made the fourth round at all the majors and played in the year-end WTA Finals. Still, that was seven years ago.

“I have been playing tennis since I was four, so quite literally been playing it for almost my whole life,” Keys said. “I have been on the tour since I was 14. I feel like I have played through a few different eras now, the tail end of some people, middle of other people and then the start of others.

“Yeah, I just feel like I have played for a long time and been around and seen a lot of different faces.”

Keys has weathered a lot over the years, including shoulder and wrist surgery as a result of the torque her shots develop. This year, too, has offered its challenges. Keys came down with shingles after the Australian Open and couldn’t eat for three weeks, losing 15 pounds. A strictly liquid diet led to food poisoning at Indian Wells.

She put together a decent clay season but lost to qualifier Kayla Day in the second round at Roland Garros. Grass, as usual, was a welcome sight. Keys won all five matches in Eastbourne, a coastal town in southeast England. The last two, against No.7-ranked Coco Gauff and No.11 Daria Kasatkina, sent her flying into Wimbledon with some much-needed momentum.

After defeating British wild card Sonay Kartal 6-0, 6-3 in the opening round, Keys has won each of her four sets and is looking to improve on her career-best effort here, a quarterfinal run in 2015. 

What’s it going to take to reach the final four here for the first time?

“Winning one more match, I guess,” Keys said, smiling. “Honestly, I’m just really not even trying to think that far ahead. I have a match most likely [Saturday], and that’s all I’m going to worry about for right now.”