Roger Federer won his first match since regaining the world No 1 ranking on Saturday against Andreas Seppi.
Federer triumphed 6-3 7-6 in the Rotterdam Open semi-final a day after reaching the summit of the ATP rankings again.
He will play Sunday's final against Grigor Dimitrov, who profited from an eye injury to semi-final opponent David Goffin when a ball struck him, causing his retirement.
David Goffin is forced to retire after the ball ricochets off his racket into his eye
Seppi caused some early trouble by matching Federer's break of serve but fell away at the end of the first set.
The world No 81 extended the second set into a drawn-out affair but Federer won the tie-break.
Federer only needed to reach the final four, which he achieved on Friday, to become the oldest ever world No 1 at the age of 36.
He also broke the record for the longest gap between his first stint at the top of the rankings and his most recent, after first achieving the landmark 14 years ago.
Federer accepted a wildcard entry in Rotterdam and took advantage of previous world No 1 Rafael Nadal's absence to overtake him.
Watch Federer vs Dimitrov in the Rotterdam Open final on Sunday, live on Sky Sports Arena from 2:30pm.