Halle Westfalen - German star Alexander Zverev said he needed more practice on grass after beating Dutchman Robin Haase 6-4, 7-5 to reach the second round of the ATP tournament in Halle on Monday.
Second seed Zverev came back from 5-2 down in the second set to record his first grass court victory of the season, following an early exit in Stuttgart last week.
"The start of the grass season is always a bit tricky. You need practice to get used to the conditions," said Zverev.
World number five Zverev, who won the ATP Finals in London last year, is among the favourites in Halle alongside nine-time winner Roger Federer
Federer faces Australia's John Millman in his first-round game on Tuesday, while Zverev can now prepare for a second-round clash with American Steve Johnson, who beat Philipp Kohlschreiber 6-3, 6-3 earlier in the day.
"Steve is someone who has a very good serve and is very good on grass. There are no easy matches here," said Zverev.
Third seed Karen Khachanov is also in the second round after beating Serbia's Miomir Kecmanovic 7-6 (7/5), 6-4.
France's Pierre-Hugues Herbert sprung a minor surprise as he beat veteran compatriot Gael Monfils 7-6 (8/6), 6-4.
Elsewhere, Moldova's Radu Albot came from behind to win 5-7, 6-1, 6-4 over Australia's Matthew Ebden and Portugal's Joao Sousa recorded a 7-6 (7/3), 6-1 win over Poland's Hubert Hurkacz.
Results from the ATP tournament in Halle on Monday (x denotes seeding):
Alexander Zverev (GER x2) bt Robin Haase (NED) 6-4, 7-5
Karen Khachanov (RUS x3) bt Miomir Kecmanovic (SRB) 7-6 (7/5), 6-4
Joao Sousa (POR) bt Hubert Hurkacz (POL) 7-6 (7/3), 6-1
Steve Johnson (USA) bt Philipp Kohlschreiber (GER) 6-3, 6-3
Radu Albot (MDA) bt Matthew Ebden (AUS) 5-7, 6-1, 6-4
Pierre-Hugues Herbert (FRA) bt Gael Monfils (FRA x5) 7-6 (8/6), 6-4