The transition to the seniors tour proved difficult for Mergea. After turning pro in 2003, he struggled to make a breakthrough. Injuries hampered his career and in spite of reaching no. 103 in the doubles rankings, his lack of singles success and limited support drained his motivation. In 2010, Mergea decided to retire from tennis, a decision he turned around months later, with the help of his wife, Daiana. With renewed focus on the doubles game, his rankings rose steadily, playing alongside the likes of Andrei Daescu and Philipp Marx. After reaching thirteen challenger finals within little over a year, Mergea won his first ATP title in October 2013, when he teamed up with Lukas Rosol for the Erste Bank Open, Vienna.