Amanda Anisimova suffered a shock exit at the Brisbane International as Marta Kostyuk soared into the quarter-finals.

The pair had trained together earlier in the week, but it was Kostyuk who came out on top on centre court, with a 6-4 6-3 victory in just under an hour and a half.

The Ukrainian held off a break point early on, and though she gained the advantage in the penultimate game, she had to fend off another three break points in the final game to take the set.

After going behind again in the second set, Anisimova earned a break to draw level at 3-3, but she failed to win another game after that, with Kostyuk cruising over the line.

"It's unbelievable," Kostyuk said. "I practised with Amanda a week ago, and she destroyed me, so I was coming into this match super ready, but she's a great player, and she had an amazing season last year.

"I didn't have the best season last year, so I'm very happy to start like this."

What it means @marta_kostyuk secures her spot in the quarterfinals!#BrisbaneTennis pic.twitter.com/ZjceRuCNJ0

— wta (@WTA) January 8, 2026

Kostyuk will now take on Mirra Andreeva in the final eight, after the Russian overcame a scare against Linda Noskova in her round-of-16 clash.

The 18-year-old lost the first set but rallied to a 5-7 6-4 7-5 victory in two hours and 24 minutes, while fending off two match points in the final set at 5-4 down.

Elsewhere, Jessica Pegula also needed a comeback victory to make it through to the quarter-finals.

She triumphed 5-7 6-2 6-3 against Dayana Yastremska, doing it the hard way after failing to close out the first set when leading 5-4 with a break.

Data Debrief: Kostyuk serves in style

Kostyuk took the game to Anisimova, with her impressive performance on serve going a long way to helping her win, as she hit six aces.

She also won 76% of her first-serve points (31/41) compared to 65% for Anisimova, and saved five of the six break points she faced (83%).