NEW YORK, NY, USA - In many a major tournament press conference "older and wiser" is a familiar refrain from the players at the podium. But for 19-year-old Marketa Vondrousova, age is relative as she stands 18 months removed from the first WTA title she won at 17, now on the precipice of a first Grand Slam quarterfinal at the US Open.

"I'm mentally getting better," Vondrousova said after her shock win over Western & Southern Open champion Kiki Bertens. "I'm a year older, that's maybe the thing."

Per WTA Stats and Information, Czech teenager is the youngest Czech player to make the second week at a major since Nicole Vaidisova in 2005. It's the latest highlight in a career that has already had its share of peaks and valleys.

"I didn't have best season, but I think this is coming back for me. This is my life result, so I'm very happy. I think hard work has paid off."

- Marketa Vondrousova

"I’d play for three days, and then I’d stop, because my elbow was hurting," she recalled back at the BNP Paribas Open. "Then again, and again. It was on my left arm, so I couldn't serve, play, or anything. I just did fitness, running, and I think that helped me. I started playing 15Ks, then I won Biel."

Vondrousova grins and breaks into a laugh.

"It was fast, but I’m used to it now."

Winner of back-to-back Grand Slam junior doubles titles, she missed most of 2016 with that same injury, only to come back to an immediate 20-match winning streak and two titles on the ITF Pro Circuit level.

She qualified for just her second-ever WTA main draw two months later in Biel/Bienne - beating Aryna Sabalenka along the way - and blitzed the field with wins over countrywomen Kristyna Pliskova and Barbora Strycova, becoming the youngest to win a WTA title in nearly three years (Ana Konjuh, 2015 Aegon Open).

At No.233 in the world, she was the lowest-ranked to even make a final since Justine Henin finished runner-up at the 2010 Australian Open.

"When I started playing again, I was just focused on myself, because I was just enjoying to play tennis after my injuries. I think that was the key, I just had fun and was enjoying it."

Both Strycova and WTA Legend Martina Navratilova came by to congratulate Vondrousova that afternoon in the California desert. She had just beaten Sabalenka for a second time to earn her best result at a Premier Mandatory tournament.

"I met Martina for the first time at Fed Cup, and we got a chance to speak. Barbora and I are friends. She’s so nice, and we are doing dinner sometimes."

Soon after bowing out in the fourth round of Indian Wells, Vondrousova switched from longtime coach Jiri Hrbec - who had been working with her via correspondence when she traveled to tournaments outside Europe - to Martin Fassati, just before the Porsche Tennis Grand Prix.

Between Stuttgart and the Ladies Championship Gstaad - where she brought on former ATP pro Jan Hernych and reached the semifinals - Vondrousova didn't win a single WTA main draw match.

"It was a tough summer, and I lost a few matches," she said after a straight-set win over 2014 Wimbledon finalist Eugenie Bouchard on Thursday. "My head is getting better again, so that’s really good for me."

Armed with vicious lefty spin and plenty of variety - particularly favoring her dropshot - Vondrousova came full circle at the US Open against Bertens. A year after she lost a final set tie-break to 2004 champion Svetlana Kuznetsova in the first round, she rallied from a second set slump and a break down in the third to hold off the big-hitting Dutchwoman in a similar sudden death on Louis Armstrong Stadium.

"I didn't have best season, but I think it's coming back for me. This is my life result, so I'm very happy. I think hard work has paid off."

So excited was the youngster to have won that she forgot to shake umpire Mariana Alves' hand, apologizing on Instagram later that day.

"The emotions were so overwhelming that I didn't know what was happening!" she wrote.

Two days older and plenty wiser from a fortnight of firsts, Vondrousova will next play Lesia Tsurenko for a spot in the quarterfinals.