Raonic, seeded 12th, won by scores of 6-1, 6-2 in third round action at the tournament in Key Biscayne, Fla. He survived a tougher test the past weekend, against American Jack Sock, after getting a bye into the second round.
The power-hitting Canadian fired 10 aces and lost just five points on his serve against Garcia-Lopez. He will next face either Benjamin Becker of Germany or Aljaz Bedene of Slovenia, with a potential quarter-final matchup against Rafael Nadal looming should he survive that round of 16 matchup.
Nadal is in action later Monday against Denis Istomin of Uzbekistan, with Australian Open champion Stan Wawrinka of Switzerland also scheduled to play.
The women's tournament on Monday includes matches featuring Maria Sharapova as well as past tournament champions Serena Williams, Venus Williams and Aga Radwanska.
Serena Williams is looking to win the event a record seventh time.