After counting down the Top 5 matches at WTA events in 2017, our year-end review moves to the best Grand Slam matches of the season!

No.4 comes from Down Under - as Eugenie Bouchard and CoCo Vandeweghe battled until the last ball for the right to advance to the second week at the Australian Open.  

WHAT HAPPENED: Most would've been forgiven if they didn't pencil CoCo Vandeweghe in for a deep run at the season's first Grand Slam, as the American came into the Australian Open unseeded, ranked World No.35.

After losing to qualifer Duan Ying-Ying at the Apia International in Sydney to begin her season, Vandeweghe scored a pair of victories over No.15 seed Roberta Vinci and Pauline Parmentier to match her best-ever result at the Australian Open. 

On the other side of the net in what proved to be a pivotal third-round clash not just for both players - but for the landscape of the 2017 WTA season - was Eugenie Bouchard, who looked to put a trying 2016 behind her with a clean start to the new season.

Fresh off a run to the semifinals in Sydney, the Canadian scored a pair of wins over Louisa Chirico and Peng Shuai to reach the third round - and was looking for her best showing at a Grand Slam in over a year as the two walked out on Rod Laver Arena. 

Read more: Top 5 Grand Slam 2017 Matches
(No.5): Konta vs. Vekic - Wimbledon

A single break in the seventh proved to be all that Vandeweghe needed to pocket the opening set, but the pair ended up headed to a decider as Bouchard made an early break of her own stand up in the second set.

Bouchard's momentum continued quickly to start the final set, as she opened with a love break, and held the advantage for much of the decider as the match wound through to its conclusion.

Read the match report: Pavlyuchenkova, Vandeweghe triumph in three-set thrillers Down Under

After getting back on serve, the ninth game of the third set proved key for the American: she saved four break points in a game that went to deuce eight times to move ahead for the first time in the decider. 

Before the two had a chance to play out the advantage set, Vandeweghe sealed the 6-4, 3-6, 7-5 victory in two hours, 22 minutes behind her third break of the match to become the first player into the second week in Melbourne.

The American's all-or-nothing style reaped rewards on the stat sheet as well: she held a 40-21 advantage in winners, hit 11 aces to the Canadian's four and won 85% of the points played behind her signature first serve.

WHAT THEY SAID:

Upon reaching the fourth round, Vandeweghe recognized the quality of her opposition, and the tennis that they played, despite that fact that both players came into the match unseeded.

"I don't really take rankings that much into consideration as far as when I go up and face an opponent, if I'm ranked higher or lower. Whatever, you've still got to go out there and beat them," she said. "I think she's a quality player. I think any player within the top 100 is going to be a quality player."

While fans and pundits might've not expected Vandeweghe's run to start the year, the American quickly showed she thought the opposite - an attitude that would become a hallmark of her rise up the rankings in 2017.

She added: "It was kind of expected, in my mind, to get the win and to get the victory and to move a step closer to achieving what I want to achieve for this year and also this tournament."

In defeat, Bouchard proved reflective to reporters after the match - as she attempted to compartmentalize her disappointment and look ahead to what would be a long 2017 season.

"It's hard to see positives right now, but it's definitely tough, considering I broke in the first game of the third, to always be a break ahead," she said. "I definitely felt a lot of pressure every service game because of her serve. I know she can serve big. I just kind of felt always that pressure to keep my lead, and it was tough to sustain that later on in the third.

"Coming to Australia, I think I did an okay job. I obviously, deep down, always expect more, but I couldn't expect too much considering I trained for a month, and it's the first, you know, really good training I got in a while; first time I got a good break in a while; first time I trained well in a while.

"I haven't played so many matches in three weeks in a really long time, and especially against top, highly-ranked, relatively speaking, players."

WHAT IT MEANS: Despite it being played in just the third week of the season, the third-round match proved key in the trajectory of both players in 2017.

Vandeweghe had reached the quarterfinals and the fourth round in the past two years at Wimbledon, but a third round showing in Australia in 2016 was her best result at any non-grass major until her breakout major in Melbourne.

En route to her first Grand Slam semifinal, Vandeweghe defeated Vinci, Parmentier and Bouchard, before taking out World No.1 and defending champion Angelique Kerber in the round of 16, and No.7 seed Garbine Muguruza in the quarterfinals. 

She was one set away from her first Grand Slam final after winning the opening tiebreak against Venus Williams in the last four, but the American wasn't disheartened by a three-set defeat to the seven-time major champion.

Instead, she used her early success Down Under as a springboard for the best season of her career to date, in which she rocketed up the rankings to end the year at World No.10, and reached a second Grand Slam semifinal at the US Open.

Conversely, Bouchard won back-to-back matches at WTA level just once more in 2017, and the Canadian's career swoon continued: she ended the season on a five-match skid and ranked World No.81 - her lowest in five years.