"I felt OK this morning when I practiced and decided to give it a go," Murray said. "I feel a little sore in the joints and stuff a little bit. I mean I feel tired mentally. I haven't really slept much in the last few days so that's probably catching up to me a little bit.
"But I hit the ball pretty well. After playing for eight weeks on grass pretty much, it's very different here. The ball is very quick compared with Wimbledon. It also bounces much higher. The court is much slower as well. So there are a lot of things to change."
Raonic beat Murray in the Barcelona semifinals nearly four months ago.
"Yeah, it will be tough," Murray said. "He'll obviously be motivated playing in his own country. You know he's improved a lot over the last year, year and a half. He's playing really, really good tennis. Very big guy with a big game. Serves well and hits the ball very hard."
Raonic advanced Tuesday.
"Obviously, for the first match it was a decent performance," Djokovic said. "I was struggling to find the rhythm, obviously, as most of the players who came late from London do and did.
"It's really difficult. We're not even two days here, a couple of practices and it's totally different conditions, time zone, ball bounce, everything. But I love playing on hard court. It's my surface."
In other second-round matches, fourth-seeded Tomas Berdych edged Julien Benneteau 6-7 (10), 6-4, 6-4; Jeremy Chardy upset third-seeded Jo-Wilfried Tsonga 6-4, 7-6 (4); fifth-seeded Janko Tipsarevic beat Mikhail Youzhny 7-6 (2), 6-4; Radek Stepanek topped sixth-seeded Juan Martin del Potro 6-4, 7-6 (5); Tommy Haas beat ninth-seeded Gilles Simon 6-2, 6-3; and Sam Querrey edged No. 13 Kei Nishikori 6-2, 6-3.