WASHINGTON DC, USA - Unseeded Zarina Diyas halted the run of American qualifier Coco Gauff in the opening round of the Citi Open.

Gauff was playing in her first tournament since her sensational Wimbledon heroics, where the 15-year-old made history as the youngest ever qualifier to reach the tournament’s main draw and then stunned Venus Williams en route to the fourth round.

She needed to navigate the qualifying rounds once again in the U.S. capital, where she scored two victories to reach the main draw.

Read more: Gauff cruises into Citi Open main draw

However, she never found her rhythm against the tricky Diyas, who is ranked 62 spots higher than Gauff at World No.84. Diyas needed an hour and 18 minutes to seal the 6-4, 6-2 victory and book her spot in the second round.

"I don't think it's my biggest win, but it's of course, a good win," Diyas said after the match. "She's so young, but she's a great player. I knew it was going to be tough, but I'm really happy with my win."

"I knew there was going to be a big crowd and they were going to support her. I love a big crowd even if they are against me, so I enjoyed it. 

"She's so strong. She has a great serve, and she's moving well. I think I was playing more aggressive today, and I served better."

It was nonetheless a quick start for Gauff, who was the first of the two players to break serve in the opening game of the match.

Though the Kazakh responded immediately and kept the pressure on the teenager for much of the opener, it was again the American who moved into the ascendancy with her second break of serve, as she broke Diyas to love to lead 4-3. 

That proved to be the last break that Gauff would author in the match, as she in turn dropped serve to love, and then surrendered serve for a third time to lose the set.

Read more: Coco Gauff: 'Every loss, there’s something I learn from that'

The American provided a measure of early resistance in the second set, as she saved four break points to avoid losing serve for a third straight time, but lost the last four games of the set to lose the match. 

It was a measure of revenge for Diyas in the singles, after she and partner Zhu Lin fell to Gauff and Caty McNally in the first round of the doubles draw on Monday, 6-3, 6-2.

"I think it helped me that I played her yesterday," Diyas said. "I had a feeling for her shots, I returned some serves, so it was helping me."

Up next, the Kazakh player will take on No.5 seed Lesia Tsurenko, who eased past Wang Yafan in straight sets to advance on Monday, 6-3, 6-2.

"I played her, like, three weeks ago. It was a tough match," Diyas said. "She's playing good. She's a great player, bringing a lot of balls back.

"I know how she plays, so my coach and I, we're going to prepare the plan, and I'm looking forward to it."