Bernard Tomic was beaten by Viktor Troicki in his first ATP World Tour match of the year at the Istanbul Open and former champion Martin Klizan made it through to the second round of the BMW Open on Monday.
Tomic lost to world number 233 Antoine Hoang on his return to the court in an ATP Challenger Tour event in Lille last month and suffered another blow when he went down 3-6 6-0 7-5 to sixth seed Troicki.
Wildcard Tomic, who failed to make it through qualifying at the Australian Open on home soil before a short spell on reality television show 'I'm A Celebrity… Get Me Out Of Here!', served for the match in the final set but was unable to get the job done.
Paolo Lorenzi claimed his 100th Tour-level win, the fifth seed seeing off Cem Ilkel 6-2 6-3, while Laslo Djere, Marco Trungelliti and Taro Daniel were also first-round winners.
Qualifier Klizan fought back to reach round two in Munich, defeating Florian Mayer 3-6 6-4 6-3.
The 2014 champion from the Czech Republic beat Novak Djokovic at the Barcelona Open last week before the unstoppable Rafael Nadal consigned him to a quarter-final defeat and the Slovakian broke six times to account for Mayer.
Wildcards Matthias Bachinger and Yannick Hanfmann got past Mikhail Kukushkin and Marcos Baghdatis respectively in their homeland on day one.
Frances Tiafoe saved three match points before overcoming fellow American Tennys Sandgren 3-6 7-6 (7-5) 7-6 (7-4) in round one of the Estoril Open.
Alex de Minaur and Pedro Sousa were the other winners on the clay in Portugal.