Roger Federer's return to the grass courts began with a routine 7-6 (7-1) 6-3 win over John Millman in his Halle Open opener.
Millman had beaten Federer at the US Open last year, yet the 20-time grand slam champion - bidding for a 10th title in Halle - controlled their clash on Tuesday.
Australian Millman dug in early on and reached a tie-break without facing a single break point, instead putting Federer under a little pressure in front of a nervy crowd.
But the Swiss great seized a pair of mini-breaks in succession and Millman's hard work was undone.
And with a set in hand, Federer was comfortable from there, holding with speed and confidence and leading after dictating a rally on break point as Millman lobbed wide.
The 37-year-old served out an ultimately straightforward victory despite Millman threatening a break for the first time with a pinpoint passing forehand.
Defending champion Borna Coric, who defeated Federer in the final 12 months ago, also advanced with a straight-sets win over Jaume Munar.
Meanwhile, Matteo Berrettini built on his Stuttgart Open title from last week with another impressive win over sixth seed Nikoloz Basilashvili.
Guido Pella was another seed to fall against David Goffin, but Roberto Bautista Agut got through.
Jo-Wilfried Tsonga defeated compatriot Benoit Paire, joining Richard Gasquet, Jan-Lennard Struff, Sergiy Stakhovsky and Andreas Seppi in the last 16.
At the Queen's Club Championships, rain meant there was no play on Tuesday.