Tim Henman let a two-set lead slip to lose to Guillermo Canas 7-6 7-5 6-7 5-7 7-9 at the Australian Open.
Henman took the first on a tie-break and sneaked the second 7-5.
He was unable to hold onto an early break in the third set and allowed Canas back into the match when he played a poor tie-break.
Canas took the fourth 7-5 to send it to a decider, and, despite holding an early break, Henman finally succumbed 9-7 in the fifth.
Henman at times played close to his best tennis, but questions will be asked after he again failed at a Grand Slam away from home and threw away such a promising position.
Even in the fifth set Henman had his chances, breaking to lead 4-1 before Canas levelled the match at 4-4.
The match turned when Henman led 30-0 as Canas served at 6-7 down but the Argentine produced a brilliant lob with Henman well placed at the net.
Canas escaped and then broke immediately as Henman double-faulted on break-point.
Henman bravely saved two match-points with some bold attacking play and had the chance to break back when Canas double-faulted himself.
But the Argentine found his first serve when he most needed it to get out of trouble, and sealed victory with a brilliant passing shot after an epic four hours and 51 minutes.
It is a familiar story against Canas, who previously held a 3-1 lead over the Briton including wins in the US and French Opens.
Canas now goes on to an all-Argentine clash with eighth seed David Nalbandian in the last 16.