After Juan Carlos Ferrero's defeat to Andre Agassi in the Masters Cup, Andy Roddick has been confirmed as the second youngest year-end world number one ever.
Roddick reached three Grand Slam semis, winning the US Open
Here we look back at the key matches and moments in Roddick's climb to the top of the world rankings.
22/01/03 Australian Open quarter-final
Roddick bt El Aynaoui 4-6 7-6 (7/5) 4-6 6-4 21-19
Andy Roddick's year was marked out as being special right from the start when he won this epic tussle with Younes El Aynaoui at the Australian Open.
The five hour marathon finished at one in the morning and put Roddick into a Grand Slam semi-final for the first time.
Ranked 10th in the world rankings at the start of the year, Roddick had previously seemed unable to make the big step from promising contender to potential Grand Slam winner.
An exhausted Roddick was unable to lift himself as he lost to Rainer Schuettler in the last four, but it was the first of three Grand Slam semis in 2003.
27/05/03 French Open first round
Sargsian bt Roddick 6-7 (3/7) 6-1 6-2 6-4
Roddick went to Roland Garros on the back of a tournament win on clay in St Poelten but crashed in the first round for the second year running.
"It's weird going from feeling like you're playing pretty well to not really knowing what you're doing," said Roddick after his defeat to journeyman Sargis Sargsian.
It proved the turning point in Roddick's season as it prompted him to team up with Andre Agassi's former coach Brad Gilbert two weeks later.
Almost instantly Roddick was a changed man, with Gilbert, who wrote a book entitled 'Winning Ugly', charged as the man who made the difference.
14/06/03 Stella Artois Championships semi-final
Roddick bt Agassi 6-1 6-7 (5/7) 7-6 (8/6)
A change in Roddick's game was already noticeable at Queen's, his first tournament under the guidance of Gilbert.
The young American took out Greg Rusedski and Taylor Dent, two big-serving grass-court players on his way to a semi-final meeting with Andre Agassi.
Roddick had never before beaten Agassi, but he blitzed the world number one in the first set and won the match in three.
With his confidence brimming, he went on to walk all over Sebastien Grosjean to claim the title and set himself up as one of the principal favourites for Wimbledon.
04/07/03 Wimbledon semi-final
Federer bt Roddick 7-6 (8/6) 6-3 6-3
Roddick's serene progress through the early rounds at The All England Club, including another win over a raging Rusedski, had seen him emerge as the outright favourite for the title.
In the semi-finals he faced the extravagantly gifted Roger Federer - another player looking to claim his first Grand Slam title.
Questions had previously been asked about Federer's big-match temperament, but the Swiss overwhelmed Roddick with his grass-court mastery.
So Roddick was left to rue a second Grand Slam semi-final defeat of the year, although his favoured American hardcourt swing was just around the corner.
17/08/03 Cincinnati Masters final
Roddick bt Fish 4-6 7-6 (7/3) 7-6 (7/4)
Once Roddick got onto the hardcourts of America he proved almost unbeatable.
Roddick won Masters Series titles in Montreal and Cincinnati back-to-back
In the build-up to the US Open he lost just one match out of 21, picking up three titles along the way, including back-to-back Masters Series titles - the first of his career.
His last match before the Open was the Cincinnati Masters final, in which he faced his good friend Mardy Fish.
Despite being nowhere near his best after his overwhelming schedule, Roddick dug out a gutsy victory and installed himself as the overwhelming favourite at Flushing Meadows.
06/09/03 US Open semi-final
Roddick bt Nalbandian 6-7 (4/7) 3-6 7-6 (9/7) 6-1 6-3
Everything went to plan for Roddick at Flushing Meadows until he met David Nalbandian in the semi-final and found himself match-point down in the third-set tie-break.
Typically Roddick fired an ace and went on to complete an amazing five-set comeback victory.
"At that point I was nearly down and out - I had no pressure at that point so just went for it," he said afterwards.
In the final, newly-crowned world number one Juan Carlos Ferrero proved no match, and Roddick laid the foundations that eventually helped him beat the Spaniard to the end-of-year world number one spot.