Alexander Zverev and Karen Khachanov bounced back from disappointments in Stuttgart last week to reach the second round of the Halle Open on Monday.

Second-seeded Zverev defeated Robin Haase 6-4, 7-5, while Khachanov celebrated his first match as a top-10 player with a 7-6 (5), 6-4 win over Serbia's Miomir Kecmanovic.

Nine-time champion Roger Federer is the top seed at the grass-court tournament, a warm-up for Wimbledon. Federer is due to play Australia's John Millman on Tuesday.

Both Zverev and Khachanov lost their opening matches in the Stuttgart Open. Zverev next faces American Steve Johnson, who defeated former champion Philipp Kohlschreiber 6-3, 6-3, while Khachanov awaits the winner between Jan-Lennard Struff and Laslo Djere.

Also Monday, Pierre-Hugues Herbert upset fifth-seeded Gael Monfils 7-6 (6), 6-4, while Radu Albot and Joao Sousa also won.