Viktor Troicki's poor start to the clay season continued in Munich as the Serb suffered a first-round defeat to Victor Estrella Burgos at the BMW Open on Monday.
Troicki has made a largely successful return to the ATP Tour this year and claimed his first title since 2010 at the Sydney International in January, but defeat to the Dominican was a second consecutive a first-round loss.
Having lost his opening match at the Nastase Tiriac Trophy to Daniel Gimeno-Traver last week, Troicki succumbed 7-6 (7-4) 6-4, taking his record on clay to one win and three defeats so far this year.
A tight opening set was dominated by both serves and it was Estrella Burgos who found an opening to move ahead in the inevitable tie-break.
The veteran world number 51 kicked on in the second set as he made inroads into the Troicki serve in game 10, securing by converting a second match point.
Qualifier Alexander Zverev also enjoyed Monday, coming from a set down to beat Benjamin Becker 4-6 6-1 6-2, having overcome Norbert Gombos just a few hours earlier to reach the first round.
Elsewhere, there were qualification wins for Dustin Brown, Radek Stepanek, Gerald Melzer and Mischa Zverev.