(Photo credit: Geoff Burke-Imagn Images)

Two of the top four American women's tennis players appear headed for a showdown in the round of 16 in the Australian Open.

However, No. 6 Jessica Pegula and No. 9 defending champion Madison Keys are not quite there yet.

Both veterans won their second-round matches over countrywomen in Melbourne on Thursday, as Pegula cruised past new doubles partner McCartney Kessler 6-0, 6-2 and Keys ousted Ashlyn Krueger, 6-1, 7-5.

Of course, any opponent making it to the third round of a major could pose a threat to Pegula or Keys. The reigning champ will have to face resurgent and former World No. 1 Karolina Pliskova of the Czech Republic, who knocked off Janice Tjen of Indonesia 6-4, 6-4.

Pegula might have been expecting to see No. 25 Paula Badosa on the other side of the net in the third round, but the Spainard was dismissed by Russian Oksana Selekhmeteva 6-4, 6-4.

Selekhmeteva had never been past the first round of a major championship.

Pegula teamed up with Kessler for the first time on Wednesday, but the duo dropped their opening-round doubles match.

In their singles contest, Pegula took control from the outset, playing her usual brand of controlled tennis. She hit 10 winners and made only two unforced errors in the first set, which lasted just 21 minutes.

Kessler dropped the first eight games of the match before holding serve at love and then evening the second set at 2-2 by converting her second break-point chance of the fourth game. However, Pegula broke right back and was never threatened thereafter.

'I just tried to stay loose -- got off to a really good start, which I was proud of, but then I lost it right back,' Pegula said. 'She's such a good competitor so I knew that at one point she was going to find a way to start playing better and work her way into the match.

'I think I got a little too passive at some point, but she started ripping and being a little more aggressive. I just had to adjust a little bit more, but I did a good job of not panicking and sticking to my game plan.'

Pegula won 13 of 15 points on Kessler's second serve and took the match in 58 minutes.

Keys nearly matched Pegula, winning the first set in 23 minutes. But Krueger produced three easy service games in the second set and broke Keys twice to take a 5-2 lead.

Krueger would not win another game, though. She had one set point at 5-4, but Keys rattled off three straight points to knot the set. Keys fell behind in the 12th game, but won the net three points and her ninth straight match in Melbourne.

'I think I started really well and Ashlyn started a little bit slow,' Keys said. 'And then I was fully expecting her to raise her level, which she did. It just kind of got away from me a little quickly.'

'I just wanted to, even if I lost the (second) set, make sure I tried to get back in the set and try to figure out where my game kind of went and be able to get a few more points on the board. Once I kind of got back momentum, I just tried to sink my teeth into the set and do whatever I could to get back into it.'

Keys did an excellent job on the return of serve, winning 30 of 58 points.

--Field Level Media