World number one Rafael Nadal had to save two match points before beating Viktor Troicki 7-6 (7-4) 4-6 7-6 (9-7) to reach the Japan Open final.
It took Nadal over two and a half hours to see off his Serbian opponent, who hit 26 aces during the match.
The Spaniard next faces fifth seed Gael Monfils, who had a much easier passage as he beat Radek Stepanek 6-3 6-3.
"I played well in the first set, but then I lost my concentration," Nadal said afterwards.
"The season is long and we compete with a lot of pressure, so it is easy to lose your concentration. That is what happened."
Troicki served for the match at 6-5 in the deciding set but he double-faulted, missed an easy volley and hit a forehand into the net to squander the opportunity.
Despite that, the Serb retained his composure for the tie-break and had match points at 6-5 and 7-6 before Nadal finally took it 9-7.
In Sunday's final, Nadal will be seeking his seventh title of the year, having won Wimbledon, the US Open and four tournaments on clay.
He will start as a firm favourite having won six out of seven previous meetings with Monfils - his sole defeat coming in Qatar last year.
But the Frenchman said: "I'm very motivated. I know it's going to be hard, but if I have a small opportunity I will take it."
Monfils has the chance to improve a poor career record against Nadal
Monfils knocked out Andy Roddick in the quarter-finals and after saving a break point in the sixth game against Stepanek, broke his Czech opponent twice in a row to take control of the match.
He wrapped things up after only 70 minutes on court to avenge a defeat by Stepanek in Brisbane at the beginning of the year.
"I had a shoulder problem then and I couldn't serve 100 per cent. I came out today much stronger. That made the difference," said Monfils.
"I am playing better and better. I change my game every day. Some days I'm defensive, some days I'm aggressive. Some times I'm on the net too much."
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