Newly-crowned French Open champion Rafael Nadal and five-time champion Roger Federer both enjoyed comfortable opening wins to their grasscourt season at Halle.
Nadal defeated Slovakia's Lukas Lacko 7-5, 6-1 in second round while Federer also cruised into the quarter-finals with a 6-4, 7-5 win over Germany's Florian Mayer.
Spanish world number two Nadal, playing at the German venue for the first time since 2005, will tackle German eighth seed Philipp Kohlschreiber in the quarter-finals.
Kohlschreiber, the defending champion, made last eight with a 6-7 (5/7), 6-1, 6-3 win over Poland's Lukasz Kubot.
Nadal, who captured a record seventh Roland Garros title on Monday, has won all his eight career meetings with the German.
Top-seeded Nadal last played this tournament seven years ago, fresh from his first French Open title but suffered a rude awakening on his debut on grass, losing in the first round to Alexander Waske.
Nadal took just 75 minutes to complete his fourth win against Lacko, who is one of the few players on tour to have won a set to love against the Spaniard, achieving the feat in Doha earlier this year.
World number three Federer will tackle Canadian fifth seed Milos Raonic on Friday for a place in the semi-finals of this Wimbledon tune-up event.
Federer, who missed last year's tournament, needed just 74 minutes to see off Mayer.
The Swiss star, who was champion in Halle in 2003, 2004, 2005, 2006 and 2008, was playing his first match since losing to Novak Djokovic in the French Open semi-finals.