Ajla Tomljanovic and Ons Jabeur each came back from first-set deficits to claim straight-sets wins in the US Open Round of 16 on Sunday night.

Tomljanovic, who defeated Serena Williams in the 23-time Grand Slam winner's final match, reached her second Grand Slam quarterfinal in a row with a 7-6(8), 6-1 win over Liudmila Samsonova on Louis Armstrong Stadium.

Australia's Tomljanovic ended Samsonova's 13-match winning streak with the nearly 2-hour victory. Tomljanovic came back from 5-2 down and erased eight set points in the opening set.

No.5 seed Jabeur of Tunisia also came back from 5-2 down in the first set before topping No.18 seed Veronika Kudermetova 7-6(1), 6-4. It was Jabeur's first win over Kudermetova in their four meetings.

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All four players remaining in the bottom half of the draw are first-time US Open quarterfinalists.

Here are breakdowns of Tomljanovic's and Jabeur's wins, and how they could keep their momentum rolling in the elite eight:

Ajla Tomljanovic

Self-belief is key

Last year, Tomljanovic made her first major quarterfinal at Wimbledon, and she backed it up by returning to the same round at the All-England Club this year. Tomljanovic is brimming with confidence at the majors after pulling that feat off twice successively.

Even after Williams surged in the second set of their match, Tomljanovic did not waver and took home the victory, underscoring the self-belief she has built up over the past couple of seasons.

Tomljanovic was also nearly eliminated in the round prior to that, coming within two points of defeat against Evgeniya Rodina, but she battled back there too.

Tomljanovic demonstrated that self-confidence in the first set against Samsonova on Sunday night, where she saved seven set points in an 18-minute 5-4 game, as well as an eighth set point in the decisive tiebreak.

Smart choices in rallies

Tomljanovic got into the head of Samsonova as the opening frame progressed, extending rallies until Samsonova lost the plot and, eventually, the first-set tiebreak.

The Aussie's resilience paid off, drawing an increasing number of unforced errors from Samsonova, who was desperately trying to keep her 13-match winning streak going.

Tomljanovic also frustrated Samsonova with well-placed serves, which slid quickly into Samsonova’s shallow return position. If Tomljanovic can also outfox Jabeur with solid decision-making, she can give the No.5 seed a run for her money.

Seal the second service

After a grueling 82-minute first set, Tomljanovic cruised through the second.

"Just feels really good to back up a win that I think got a lot of attention," Tomljanovic said in her post-match press conference. "It's been a really big 48 hours. I didn't really feel like myself today the whole day.

"I just felt a little bit drained. After that slow start, I just didn't want to go out like that. Picked myself up, fought back really hard, played some quality tennis after that."

Powerful Samsonova finished the match with 24 winners to Tomljanovic's nine, and the pair were nearly equal in success rate behind their first serves.

But where Tomljanovic excelled was defending her second service -- she won 59 percent of those points compared to Samsonova's 40 percent success rate. It will serve Tomljanovic well down the road if she can keep that second serve rock-solid.

Ons Jabeur

Carve out the angles

In the early stages of the first set on Sunday, Jabeur was in deep trouble against a player she was 0-3 against. Kudermetova led 5-2 and was seemingly on her way to maintaining her undefeated record against the Tunisian.

But Jabeur kept her composure and pulled her way into a decisive first-set tiebreak with her trademark variety. Jabeur started the breaker with a backhand angled winner, and she steered a forehand down the line to notch a commanding 4-0 lead.

A backhand winner down the line wrapped up a dominant tiebreak for the 2022 Wimbledon finalist. As she continues to stake her claim as a Top 5 regular, Jabeur is proving that no matter the score line, she will find exactly the right places to put the ball from whatever sector of the court she is in.

Another ace queen?

Despite failing to serve out the match at 5-3 in the second set, Jabeur held on to capture her first win over Kudermetova, breaking for the triumph after an hour and a half of action on Arthur Ashe Stadium.

Jabeur dragged herself out of trouble on numerous occasions with pristine serving at key moments. She had 11 aces in the match overall, finishing the match with a 72 percent success rate behind her first delivery. More big serves will come in handy against Tomljanovic's resilient play.

Revel in the history of the moment

Jabeur takes great pride in being a historic trailblazer for her region, becoming the first Tunisian and first Arab woman to win a title, to reach the Top 10, and to make a Grand Slam quarterfinal and beyond. She is reaching more milestones in New York, which will bolster her spirits further.

Jabeur is now the third African woman to make it into the US Open quarterfinals in the Open Era (since 1968) -- and the first from the northern part of the continent. The other African women to reach the US Open quarterfinals in the Open Era hail from South Africa: Maryna Godwin (1968) and Amanda Coetzer (1994, 1996 and 1998).

Jabeur can also look back at her history against Tomljanovic for a boost. She has a 2-0 head-to-head lead over the Aussie, including a win on the clay courts of Rome this year.