WATCH: Bianca Andreescu laughs in disbelief as she hits a smash right at Marta Kostyuk, only to get a shocking winner in response at Citi Open

Bianca Andreescu leaned against her racket and laughed in disbelief when Marta Kostyuk hit a defensive winner against her smash at the 2023 Citi Open on Monday.

The pair clashed in the opening round of the tournament, with Andreescu starting strongly and winning the first set 6-2. Undeterred, Kostyuk fended off two break points in the second set to break Andreescu's rhythm and win the set by a 6-3 margin.

In the decisive set, both players were going toe-to-toe when Bianca Andreescu hit a powerful overhead smash right at her opponent. Kostyuk dropped her racket, hitting a return in defense that, much to everyone's surprise, turned into a winner. Putting her hand to her stomach and leaning forward, Andreescu laughed in disbelief.

The WTA's official channel shared a short clip on Twitter capturing the moment and captioned it:

"top notch reaction."

Marta Kostyuk also threw her hands up, hardly believing her own response to the smash.

The Ukrainian continued to bring her A-game to the contest and saved multiple match points before winning 2-6, 6-3, 7-6.

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"There were some painful mistakes": Marta Kostyuk after reaching R2 of the Citi Open 2023

Marta Kostyuk at the 2023 Citi Open

Marta Kostyuk overcame Bianca Andreescu to reach the second round of the 2023 Citi Open.

Andreescu maintained constant pressure on her opponent throughout the match and gained three match points. However, the 21-year-old Ukranian elevated her game, particularly in the latter half of the match, and used her aggressive baseline play to her advantage.

The WTA official channel posted a short clip of the winning shot and congratulated Kostyuk on her win.

"Comeback Marta! @marta_kostyuk saves three match points and takes out Andreescu in a 2-6, 6-3, 7-6 first-round THRILLER! #MubadalaCitiDCOpen," the caption read.

In a post-match on-court interview, Kostyuk spoke about her crucial break in the final set of the match.

"I lost my chances at 4-all, there were some painful mistakes," she said. "Honestly, I didn't believe I could win this one but I was just trying to play every point and stay in the match and fight not give up."

Playing at a career-high ranking of World No. 30 this week, Kostyuk will next clash with second-seed Caroline Garcia in the second round of the Citi Open on Thursday.