Raonic won 30 of 33 first-service points and required just 71 minutes to dispatch Groth 7-5, 6-4.
Raonic and will face another Aussie, Marinko Matosevic, in the next round of the Washington event. Matosevic upset No. 15 seed Nikolay Davydenko Tuesday 6-4, 7-5.
Sixth-seeded Sam Querrey of the United States labored nearly 2 hours to get past Denis Istomin of Uzbekistan. Querrey, who had not played on a hard court since April, saved two match points en route to a 6-4, 3-6, 7-6 (11-9) victory.
Other second-round winners in America's capital were Bernard Tomic, who took down David Goffin 6-1, 6-3, and Grigor Dimitrov, who topped Xavier Malisse 7-6 (7-4), 6-4.