KEY BISCAYNE, Fla. -- Sam Querrey won in his first match as the top-ranked American, rallying past Lukasz Kubot 4-6, 6-3, 6-3. The 20th-ranked Querrey this week moved ahead of No. 23 John Isner, who hit 25 aces and beat Ivan Dodig, 6-4, 5-7, 7-6 (5).
Isner has won his past five winner-take-all third-set tiebreakers.
"I really tend to play my best in a tiebreaker, for whatever reason," he said. "I wish I could sometimes play a little better outside of that."
"When you know they aren't going to be here, then it obviously changes things a little bit," Murray said. "For tennis, it's way better if all of the top players are here. I think we have been very lucky the last few years especially that a lot of the top players have fulfilled their commitments to all of the big events. So it's going to happen from time to time, and it's unfortunate for this event that it happened here."
Tomic, who fell to 2-15 against top-10 opponents, drew jeers from the stadium crowd during his lackluster performance.
Agnieszka Radwanska, seeded fourth, lost serve seven times and needed nearly 2½ hours to beat Magdalena Rybarikova 7-6 (5), 2-6, 6-3. Radwanska will next play 20-year-old Sloane Stephens, who advanced when Venus Williams withdrew with a back injury.
"I'm a little bummed, but I guess a win is a win," Stephens said. "On to the next round."
"Definitely a little bit of a rough start," the No. 1-ranked Williams said. "It was good to get through this match."
No. 9 Caroline Wozniacki lost to wild card Garbine Muguruza of Spain, 6-2, 6-4.
Querrey lost his first service game but held the rest of the way and hit 12 aces against Kubot. The 25-year-old Querrey said being the top-ranked American has provided only a modest boost in confidence.
"Some days more than others," he said. "I never thought about it out there today. Haven't really thought about it much. Felt like another day out there to me. Nothing new."
Querrey won despite a lack of rest. He's staying near downtown Miami, site of a weekend electronic music festival.
"I'm not sleeping well because of this Ultra Festival going on," he said. "I could hear the bass, and strobe lights were shining in my hotel, so it's hard to sleep."
Isner said the festival hasn't bothered him.
"I can sleep through anything," he said. "I can sleep through a train wreck. Do not hear it, which is good."