Four-time champion Andy Roddick battled past Spain's Feliciano Lopez in a high-quality second-round match.
With top seeds Rafael Nadal and Andy Murray involved in doubles action, ahead of their opening singles matches on Wednesday, the focus on day two fell on Roddick and his first match of the year on grass.
The 28-year-old American, who had a bye in round one as the third seed, faced a significant test against Spanish serve-volleyer Lopez but came through a tight contest 7-6 (7-2) 6-7 (5-7) 6-4.
Roddick was playing for the first time in a month after pulling out of the French Open with a shoulder injury. He was also looking for his first win anywhere since March.
Lopez, twice a Wimbledon quarter-finalist, had impressed in his opening win over Dmitry Tursunov on Monday and fired down 35 aces against Roddick. But, after the first two sets were split on tie-breaks, Roddick recovered from a break down to take the decider.
The American responded with a love break after dropping serve at 1-1 and clinched victory in game 10 with some superb returning, his passionate celebration illustrating how much the result meant to him.
"I love it on grass and am so happy to be back on it," he said after a welcome two-hour-25-minute contest. "I feel good.
"I'm so happy to be back in London. This is one of my favourite tournaments in world.
"As for this match, I played to win. Of course, we come over to prepare for Wimbledon but we're trying to win this tournament."
Former US Open champion Juan Martin del Potro had opened play on Centre Court with a 6-4 6-2 win over Denis Istomin of Uzbekistan, the world number 61.
Del Potro is seeded 12th at Queen's as he makes his way back up the rankings after missing most of 2010 with a serious wrist injury but most observers see the 6ft 6in 22-year-old as a potential rival to the world's top four when back to full match sharpness.
The next few weeks might not see the very best of him, though. He has never been past the second round in three trips to Wimbledon and one previous appearance at Queen's.
And several slips on the slick grass on Tuesday suggested he is still not completely comfortable on grass.
A nasty fall when reaching to return serve midway through the second set was a real alarm but, after having his thigh taped, Del Potro's heavy game and potent serve worked well enough to despatch Istomin in one hour and 23 minutes.
There were also straight-sets wins for Fernando Verdasco, Jo-Wilfried Tsonga, David Nalbandian and Xavier Malisse, who will face Murray in round two, with defending champion Sam Querrey taking three sets to beat Rainer Schuettler.
In the doubles on Tuesday, Murray and brother Jamie were beaten 6-3 6-4 by Malisse and Ken Skupski, while French Open champion Nadal and Lopez defeated Thomaz Bellucci and Andre Sa 7-6 6-2.