SINGAPORE -- US Open and Miami Open champions Ashleigh Barty of Australia and CoCo Vandeweghe of the United States continued their exceptional year by reaching the semifinals of the BNP Paribas WTA Finals Singapore presented by SC Global after a 6-1, 6-4 victory over No.4 seeds Elise Mertens of Belgium and Demi Schuurs of the Netherlands.

"CoCo and I, we kind of snuck in at the last minute, so we’re here to really just enjoy it and have fun, and try and finish the season on a high," Barty told the media after the match.

Both Barty and Vandeweghe move into the final four at the WTA Finals for the first time. Vandeweghe is debuting in Singapore, while Barty fell at the first hurdle last year partnering her compatriot and long-time teammate Casey Dellacqua.

"It’s a little bit of yin and yang with CoCo and I," Barty added. "It’s really good energy. At times, I probably need to calm her down, and other times she pumps me up, so I think it works pretty well."

The unseeded duo join the Top 3 seeds in the semifinals, and they will be matched up against No.2 seeds and Australian Open champions Timea Babos and Kristina Mladenovic, in a rematch of the US Open final. The Hungarian/French duo won their quarterfinal over Gabriela Dabrowski and Xu Yifan earlier on Friday.

"[Babos/Mladenovic is] a quality team, absolutely one of the most dominant teams throughout the whole year," Barty admitted. "US Open [is] a little bit different conditions -- the roof was closed, but it’s a little bit different in here. There’s a few similarities, but we’ll just go into it and try be nice and aggressive, and use some of the tactics that worked well for us in the Open."

CoCo Vandeweghe (L) and Ashleigh Barty in action against Elise Mertens and Demi Schuurs at the 2018 WTA Finals. (Getty)

Barty and Vandweghe dominated in the opener, racing to the one-set lead without facing a break point. Schuurs was broken first at 2-1, after Vandeweghe controlled the rallies with her overwhelming forehand. The American continued her impressive play with an easy hold to garner a 4-1 lead.

The Belgian was broken in the next game after falling behind 0-40, and then firing a forehand long on the second break point. A missed service return by Schuurs in the next game handed Barty and Vandeweghe the set. Each team had five unforced errors in the opening frame, but Barty and Vandeweghe out-winnered their opponents by eight to two.

Mertens was broken to open the second set, but the Belgian/Dutch duo finally converted a break point in the subsequent game after a beautiful forehand passing shot winner by Mertens. Schuurs and Mertens both evaded break points in their next service games to hang with the leaders en route to 3-3.

But more aggressive play by Barty and Vandeweghe allowed them to reclaim the break lead, taking the Schuurs serve for 4-3. That would be the decisive break as they rolled to victory, culminating in a powerful love service hold by the American. The victors ended with 17 winners to only 12 unforced errors, while the Belgian/Dutch duo finished with seven winners and 16 miscues.