Top seed Andy Murray struggled to a 7-6 (8), 7-6 (1) victory over Nicolas Mahut of France to begin the defense of his title at the Queen's Club on Tuesday.
Second seed Stan Wawrinka lost to Spanish left-hander Fernando Verdasco 6-2, 7-6 (3), but there were victories for fifth seed Croat Marin Cilic, who rallied to beat Spain's Feliciano Lopez 4-6, 6-3, 6-4, and sixth seed Roberto Bautista Agut of Spain, who outlasted American Sam Querrey 7-6 (2), 6-7 (4), 7-6 (1).
Third seeded Canadian Milos Raonic, watched by John McEnroe who is coaching him during the grasscourt season, surrendered the first set to Australian Nick Kyrgios in a tiebreaker but took the second 6-4 before the match was suspended due to darkness.
Murray fought off a set point before securing the opening set on his third set point, and then held off a further challenge when Mahut served for the second set at 5-3.
"It was a good win," said Murray. "Nicolas is a very good grass court player, coming off winning an event just yesterday. So he's confident and has played a lot on the grass.
"I haven't really hit many balls on the grass the last few days, and the balls that I have hit there's been very little, limited movement not being able to play any points really at all. So to get a win against a player as good as him on grass, not loads of preparation, is a good win."
Wawrinka is working with 1996 Wimbledon champion Richard Krajicek during the grass-court season, and their partnership got off to a rocky start as Verdasco broke serve in the opening game and took control of the set with a second break to lead 4-1.
In a match that was delayed by rain, the second set went with serve until Verdasco clinched victory in the tiebreaker.
"Grass court, it's always a challenging surface for my game," said Wawrinka. "I need quite a lot of practice to play my best game. Today Fernando was playing well, was playing aggressive. When the grass is quite fast, you need to be the aggressive player. He was better than me today."
Verdasco expected the challenging conditions and was happy with the way he dealt with them.
"In general I served well," said Verdasco. "You know, in general I felt very good with all my game. I think that I played a pretty good match and I'm very happy of the way I played."