The hard-court swing is in full action in Cincinnati as many top names made their hard-court debut. These are the Top 5 photos from Tuesday's action.
1. Venus Willams pulled out a 6-3, 3-6, 7-6 (4) upset over defending Cincinnati champion Kiki Bertens on Tuesday. The seven-time Grand Slam champion is into the third round after sealing her second Top-5 win of the season. The world No. 65 will take on Victoria Azarenka or Donna Vekic next.
2. Novak Djokovic dominated in his first match back since capturing his fifth Wimbledon title. The Serbian won a tight first set and then rolled through to win, 7-5, 6-1, over American Sam Querrey. The world No. 1 has reached the final of three of his last four tournaments.
3. Madison Keys battled through a rollercoaster match against Garbine Muguruza to claim her Cincinnati opener, 6-7 (4), 7-6 (5), and crack a three-match losing streak. Keys also faced the two-time Grand Slam champion last year in the first round and had a similar three-set victory. The American will battle Daria Kasatkina for a spot in the tournament's third round.
4. American Frances Tiafoe posted a, 7-6 (7), 6-3, upset against world No. 15 Gael Monfils in his Cincinnati opener. The 21-year-old is looking to capture some winning rhythm in the hard-court swing, since he has fallen early in his last two events. Tiafoe will have another opportunity to take down another Top-15 opponent when he faces Roberto Bautista Agut on Wednesday.
5. Seven-time Cincinnati champion Roger Federer made his hard-court debut against Juan Ignacio Londero on Tuesday. The Swiss easily captured the first set and at, 2-2, in the second set rain suspended play. They returned to the court later in the evening with Federer cruising to the finish line, 6-3, 6-4.