Andy Murray signalled an impending shift at the top of British tennis by beating number one Tim Henman 6-2 5-7 7-6 (7-4) at the Swiss Indoors.
The 18-year-old Scot had the better of a lacklustre Henman as he broke him twice to take the opening set in Basel.
But Henman rallied, showing glimpses of his class as Murray faltered, and made the decisive break to level the match.
The tense contest had to be settled by a tie-break and Murray produced the best shots to claim a landmark win.
Murray goes on to face 20-year-old world number 52 Tomas Berdych of the Czech Reoublic, who beat George Bastl 5-7 6-4 6-2.
"This is a pretty special day for me and I'll remember it for the rest of my life," Murray told BBC Radio Five Live.
"To win against someone like Tim, who inspired me to play the game is definitely the biggest of my career.
"If it wasn't for Tim I wouldn't be playing. I tried not to show emotion but at the end I couldn't hold it in."
Murray, playing his compatriot for the first time, made his intentions clear by totally dominating the opening set with an impressive array of shots.
The teenager broke Henman in the very first game as the 31-year-old sixth seed struggled to find his rhythm and range.
Things did not improve for Henman, who made 25 unforced errors to Murray's 11.
The more mistakes he made, the better Murray got and the Scot strolled to a one-set lead in 34 minutes.
The lifeless atmosphere inside a half-full St Jakobshalle did little to lift Henman but he certainly rallied in the second set.
The British pair swapped breaks as the topsy-turvy match opened up into a contest.
This time a series of Murray mistakes handed Henman two break points and he seized the first to level at one-set all.
The decisive third set played out in a more sedate but scrappy fashion as both players survived threatened breaks of serve.
Murray slid to deuce in the 12th game but managed to force the tie-break after making Henman chase around the court.
The Scot took a 3-0 advantage as Henman was bamboozled by a bad bounce off the net.
And though Henman fought back, Murray held on to the momentum and sealed the win with a deft forehand.
It was the first time Henman had lost to a British player since he was defeated by Greg Rusedski in Germany in 1998.
"It's frustrating and disappointing," said Henman.
"I don't think I dealt with it as well as I have done in the past. I think Andy was the one who handled it better.
"I didn't get off to the start I would like and I did well to turn it around at the end of the second set when he was serving for the match.
"I really wanted to kick on from there but it never really happened for me."
In other matches, former champions Guillermo Coria and David Nalbandian and fellow seeds Dominik Hrbaty and Jiri Novak all advanced in straight sets.