Top-seeded Serena Williams survived a tough test on Wednesday afternoon, overcoming Kiki Bertens 7-6(5), 6-3 to advance to the third round. Williams' next opponent in her pursuit for the Calendar Grand Slam is compatriot Bethanie Mattek-Sands.

Extremely Tight First Set Goes the Way of the World Number One

To begin the match, Williams held comfortably at 30. The world number one had played well in recent weeks and was looking to get another win under her belt. However, it was clear that Bertens was not going to give Williams an easy day at the office. Holding at 15, the Dutch woman got on the board to stay leveled with the 21-time Grand Slam champion.

Now tied at one, Bertens' flat hitting was catching Serena by surprise as the Dutch number one earned herself three break point opportunities. She needed all three opportunities but at the third time of asking, the world number 110 managed to go up an early break on Williams, thanks to a stunning running forehand down the line passing shot. Now up 2-1, Bertens managed to hold her own and she was not afraid to go toe-to-toe with the best women's tennis player in the world. In the end, it was the underdog who consolidated the break to go up a 3-1 lead.

From there, the server managed to win the next five games of the match and Bertens found herself up 5-4, and had a chance to win the opening set. After serving and hitting really well all set, the Dutch woman began to get tight as she made a number of unforced errors while serving for the set. As a result, the world number one was able to recover the early break to level the first set at five games apiece. In the next game, both women were not willing to give other an inch as Williams had numerous chances to close out the game and Bertens had a break point to go up 6-5. In the end, it was the 21-time Grand Slam champion who won the game after four deuces, to go up 6-5.

Now with the pressure firmly put on her shoulders, Bertens began to crumble as she went down 15-30. Nonetheless, the world number 110 continued to put up a great fight, and her efforts were rewarded as she held to 30. This meant this first set had to be decided in a tiebreak.

In the tiebreak, Bertens raced out to a sizeable 4-0 lead but Williams refused to give up, showing everyone the resilience that won helped her win her second "Serena Slam". Clawing her way from 0-4 down, Williams won five points in a row to go up a 5-4 lead in this tiebreak. A few costly and shaky unforced errors from the Dutch woman let the world number one back into this seven point shootout.

Bertens managed to hold her first service point to level the tiebreak at 5-all but Williams forced an error off of the racquet of the Dutch woman to earn her first set point, up 6-5 in the tiebreak. On Serena's first set point, the American had some extra luck on her side as a forehand caught the tape and rolled over. Bertens ran as fast as she could to get it back but she overhit it a forehand and Williams had won the opening set, 7-6(5). As you would expect, the world number one was very fired up, and the crowd were on their feet. They had just witnessed one of the best sets of tennis of the entire tournament.

Cleaner Second Set from Williams

The second set began just like the first as Bertens saved a break point and held, sending a clear message to Williams that she was not going to go away any time soon. Williams replied with a hold of her own, at love. Now tied at one, it seemed like Serena had found a new gear in this match as she broke the Dutchwoman to love. Now up 2-1, the world number one looked to be running away with this match but the resistance and fight in Bertens refused to go away as the Dutch number one broke straight back.

In the next game, Williams earned herself two break points; the first was saved with an ace but she converted the second one thanks to a double fault from Bertens. Now up a set and 3-2, Serena was beginning to run away with the match. 3-2 became 4-2 in a matter of two and a half minutes as the six-time U.S. Open champion held to love and consolidated the break. Bertens replied with a love service hold of her own and things were beginning to get a little interesting on Arthur Ashe Stadium...

The world number one has been in this situation countless times in her career and her experience was showing against the 23-year-old Dutch woman. Williams continued to maintain her lead as she held to 15 to go up a 5-3 lead. Two double faults in the next game from Bertens gave Williams two match points.

The first was saved with a forehand winner from the world number 110 but on the second one, the woman from Wateringen, Netherlands missed a cross-court backhand and Serena had sealed the 7-6(5), 6-3 win! Being the perfectionist that she is, the world number one looked rather disgusted with her performance after the match but on the bright side, the 21-time Grand Slam champion is now only five matches away from winning her 22nd major and the rare Calendar Grand Slam.