Australian Open 2021 Results: Winners, Scores from Thursday's Singles Bracket

Sofia Kenin's title defense at the Australian Open lasted two rounds.

The fourth-seeded American did not look her best in a straight-sets loss to Kaia Kanepi, which was the first major upset in Melbourne.

Kenin's defeat Thursday was the only surprise to happen in the women's bracket. Eleven seeded players, including top-ranked Ashleigh Barty, made it through to the third round. Barty was one of eight seeded women to win in straight sets.

Rafael Nadal faced little difficulty advancing on the men's side, as he cruised to a three-set triumph over Michael Mmoh. Nadal's straight-sets victory was an outlier in performances by seeded men, as a handful were pushed into the fourth and fifth sets.

Stefanos Tsitsipas survived the biggest upset bid on Thursday, as he knocked out Thanasi Kokkinakis in a five-set marathon.

Top Men's Results

No. 2 Rafael Nadal def. Michael Mmoh, 6-1, 6-4, 6-2

No. 4 Daniil Medvedev def. Roberto Carballes Baena, 6-2, 7-5, 6-1

No. 5 Stefanos Tsitsipas def. Thanasi Kokkinakis, 6-7 (5-7), 6-4, 6-1, 6-7 (5-7), 6-4

No. 7 Andrey Rublev def. Thiago Monteiro, 6-4, 6-4, 7-6 (10-8)

No. 9 Matteo Berretini def. Tomas Machac, 6-3, 6-2, 4-6, 6-3

No. 16 Fabio Fognini def. Salvatore Caruso, 4-6, 6-2, 2-6, 6-3, 7-6 (14-12)

No. 19 Karen Khachanov def. Ricardas Berankis, 6-2, 6-4, 6-4

No. 21 Alex de Minaur def. Pablo Cuevas, 6-3, 6-3, 7-5

Mackenzie McDonald def. No. 22 Borna Coric, 6-4, 6-2, 4-6, 6-4

No. 24 Casper Ruud def. Tommy Paul, 3-6, 6-2, 6-4, 7-5

No. 28 Filip Krajinovic def. Pablo Andujar, 6-2, 5-7, 6-1, 6-4

Feliciano Lopez def. No. 31 Lorenzo Sonego, 5-7, 3-6, 6-3, 7-5, 6-4

Nadal and Daniil Medvedev asserted their dominance at the end of Thursday's play.

Nadal made quick work of Mmoh, starting with a 6-1 victory in the first set. The Spanish southpaw won 60 percent of receiving points over those seven games.

Mmoh played better tennis in the second and third sets, but he never challenged the No. 2 seed, who has won six straight sets to open his title quest.

Medvedev delivered 13 aces throughout his straight-sets win over Roberto Carballes Baena. The fourth-seeded Russian took 86 percent of the points on his first serve and won seven of his eight break-point opportunities.

Tsitsipas faced the toughest test of the top men's players in action on Thursday, as he needed five sets to eliminate Kokkinakis.

The fifth-seeded Greek struggled on Kokkinakis' serve, as he won five of 22 break points and 34 percent of his 207 receiving points. Tsitsipas admitted after the match that he needed to do better in that area of his game, per ATPTour.com:

"Even though the court was slow, I had difficulties returning. ... [There were] lots of missed opportunities, break points that I had. He just managed it really well. He's capable of a lot of things. He played phenomenal tennis. I didn't have the best start in the match. [It] took me a while to get used to the rhythm, the pace. ... My fighting spirit was there."

Borna Coric and Lorenzo Sonego were the only seeded men to fall Thursday. Coric's defeat came at the hands of American Mackenzie McDonald, who is one of two Americans left in the men's singles draw.

Top Women's Results

No. 1 Ashleigh Barty def. Daria Gavrilova, 6-1, 7-6 (9-7)

Kaia Kanepi def. No. 4 Sofia Kenin, 6-3, 6-2

No. 5 Evina Svitolina def. Coco Gauff, 6-4, 6-3

No. 6 Karolina Pliskova def. Danielle Collins, 7-5, 6-2

No. 11 Belinda Bencic def. Svetlana Kuznetsova, 7-5, 2-6, 6-4

No. 18 Elise Mertens def. Zhu Lin, 7-6 (10-8), 6-1

No. 21 Anett Kontaveit def. Heather Watson, 6-7 (5-7), 6-4, 6-2

No. 22 Jennifer Brady def. Madison Brengle, 6-1, 6-2

No. 25 Karolina Muchova def. Mona Barthel, 6-4, 6-1

No. 26 Yulia Putintseva def. Alison Van Uytvanck, 6-4, 1-6, 6-2

No. 28 Donna Vekic def. Nadia Podoroska, 6-2, 6-2

No. 29 Ekaterina Alexandrova def. Barbora Krejcikova, 6-3, 7-6 (7-4)

Kenin was upset by an in-form Kanepi.

The Estonian dominated throughout the two sets in which Kenin made plenty of uncharacteristic mistakes with her shots down each baseline.

Kanepi produced 22 winners and 17 unforced errors compared to 10 winners and 22 unforced errors from the reigning champion. Kenin had seven break-point opportunities, but she failed to convert on any of them through two sets. After the defeat, Kenin acknowledged her game was off, per ESPN.

"I obviously felt like I'm not there 100 percent—physically, mentally, my game," she said. "Everything just feels real off, obviously. It's not good. I mean, I J just—I know I couldn't really handle the pressure."

Kenin's defeat opened up an opportunity for fellow American Jennifer Brady to make another deep run at a hard-court major. Brady advanced to the U.S. Open semifinals and is the highest remaining seed in that quarter in the top half of the draw.

The No. 22 seed lost just seven games in her first two matches, and she is one of five American women to advance to the third round.

Navigating through the other parts of the bracket will be difficult for some seeded players, as seven of the eight ranked women in the top two quarters advanced to the third round.

Barty faced some trouble in the second set against Daria Gavrilova, but she battled through a tiebreak to remain perfect through four sets in Melbourne.

Elina Svitolina and Karolina Pliskova were among the other top seeds who won in two sets Thursday. Barty, Svitolina and Pliskova all face seeded opponents in the next round.

Follow Joe on Twitter, @JTansey90. Statistics obtained from AusOpen.com.