Novak Djokovic had to work hard against Belgian qualifier Olivier Rochus to reach the Halle tournament final with a 7-6, 6-4 win on Saturday.
The Serbian world number four will play Germany's Tommy Haas, who earlier beat Philipp Kohlschreiber in three sets.
Djokovic, who has struggled to find his feet on grass all week, squandered a 4-1 lead and then missed three set points at 5-4 before Rochus carved out two for himself in the tiebreak.
Second seed Djokovic, who littered the court with 21 unforced errors in the first set alone, kept his composure to clinch it on his fourth set point when the 136th-ranked Rochus sent a backhand sailing wide.
Rochus, who had been troubled by a shoulder injury for the past two years and underwent surgery late last year, was broken at 2-2 in the second when Djokovic's baseline play started to come together.
The Belgian refused to give up, though, earning a break point at 4-3 before the 22-year-old Serb's thundering serve carried him to a 5-3 lead.
Djokovic served out the match two games later on his third match point.
Former world number two Haas was also stretched in his semi-final against Philipp Kohlschreiber, having to fight back from a set down to win 2-6, 7-6, 7-6.
Haas, ranked 41st, has reached his first final in more than two years after missing most of 2008 with a shoulder injury.
World number 24 Kohlschreiber, who beat Haas at Halle last year in their only other meeting, broke twice in the first set to go 5-2 up and then fired two aces to clinch it.
Both players held serve in the second to trigger a tiebreak with 31-year-old Haas getting the better of his opponent.
Haas fought back from 4-1 and 5-2 down in the third to force a tiebreak and won it on his third match point with an ace.
