To mark the end of a record-setting 2019 season, wtatennis.com is counting down our picks for the best matches of the year.

Top 5 Grand Slam Matches of 2019:
No.5: Barty d. Anisimova, Roland Garros

Continuing the countdown in the Grand Slam category at No.4 is Bianca Andreescu's statement win over Elise Mertens at the US Open, which brought her one step closer to a historic major title.

WHAT HAPPENED: The summer of 2019 belonged to Canadian teenager Bianca Andreescu, who, ironically, had missed most of the spring due to injury. Returning from a shoulder issue that forced her out of the French Open, Andreescu returned at her home tournament in Montréal, where she backed up her breakout BNP Paribas Open win with a second title at the Rogers Cup.

Despite not losing a completed match since the Abierto Mexicano Telcel, she was nonetheless an outsider pick heading into the US Open, a tournament she'd lost in the first round of qualifying the year before, and began her campaign far from Arthur Ashe Stadium on Court 10. Seeded No.15, she surged into the second week without dropping a set, and secured her first Grand Slam quarterfinal in a topsy-turvy three-setter over American upstart Taylor Townsend.

The 19-year-old returned to Ashe two nights later to play Qatar Total Open champion Elise Mertens for a spot in the semifinals. Mertens had reached the final four at the Australian Open in 2018, and represented the first big test for the crafty Canadian.

Mertens blasted through the opening set, tearing through the court with effortless power as she threatened to end Andreescu's then-11-match winning streak in perfunctory fashion.

With those watching and wondering if Andreescu could stand up to the still-new level of Grand Slam pressure, the teenager scored an impressive break to love with the help of a formidable forehand return.

Leveling the match with another winner off that wing, she and Mertens battled through a tense decider that saw the Belgian save six break points through the first seven games. Andreescu invoked all of her variety to remain ahead on serve and finally converted her seventh opportunity behind a deep backhand drive.

Andreescu found herself undaunted by the prospect of serving for a first Grand Slam semifinal, securing victory in just over two hours with a searing backhand down the line.

Read the match report: 'All of us dream of this moment' - Andreescu ousts Mertens to clinch first Slam semifinal at US Open

WHAT THEY SAID: Andreescu channeled a bit of "David After Dentist" after her winning, asking her family, "Is this real life?" as she booked her - at the time - best-ever result at a major tournament.

"I couldn't really believe it at that moment," she explained after the match. "But then when I sat down, I just couldn't stop smiling, like I can't now."

The ever-quotable Canadian opened up about the struggles that kept her from making good on the promise she showed in Indian Wells, and what ultimately kept her going.

"It took a lot of hard work. The passion's always there, though. Even through the tough times I try to stay as optimistic as I can.

"If someone told me that I was going to be in the semifinals of the US Open a year ago, I would say, You're crazy. So I'm just really proud of myself with how I dealt injury-wise while I was injured. I kept that passion going."

Read more: 'These Canadians are wilding!' - Andreescu rivals Halep in fan support in US Open debut

Mertens pointed to Andreescu's youth as a factor in her rise, crediting the teen's aggression as what turned the tide in their quarterfinal clash.

"She's still young, no pressure. I think if you can serve well at the big moments, she can do well at the big moments. That's maybe something she does very well.

"She also gets that one more strike. She's a very powerful hitter but also a good mover."

In photos: Bencic, Andreescu complete US Open semifinal cast

WHAT IT MEANT: The match ended up being crucial for Andreescu and Mertens, both of whom, ironically enough, went on to win the US Open.

While Andreescu roared through her final two matches against Belinda Bencic and Serena Williams - stopping the latter from capturing her elusive 24th major title - Mertens partnered good friend Aryna Sabalenka to win her first major in women's doubles.

Speaking of debutantes, Andreescu became the first Canadian to win a major singles title in stunning fashion against Williams, shaking off a second set hiccup to not only win but also become a Top 5 player - moving up a total of 10 spots in two weeks.

Andreescu and Mertens played again at the China Open, the former's first tournament since Flushing Meadows. In another battle, Andreescu rallied from break deficits in both sets - saving a set point in the second - to defeat the Belgian in a second set tie-break en route to clinching a debut berth at the Shieseido WTA Finals Shenzhen.