Roy Keane's Celtic debut ended in shock defeat as the Scottish Cup holders were humbled by Clyde at Broadwood.
Clyde twice had the ball in the net only for the officials to cruelly rule against them before Craig Bryson headed the First Division side in front.
Celtic 'keeper Artur Boruc then saved a penalty from Stephen O'Donnell only for Eddie Malone to stun the visitors with a volley into the top corner.
Maciej Zurawski struck late for Celtic but Clyde held on for a famous win.
Clyde, who ran Rangers close in the CIS Cup, were outstanding for the first hour and Graham Roberts' side were worthy winners.
Keane had a very quiet game as the SPL leaders struggled to cope with their eager opponents and a badly rutted pitch.
Chinese defender Du Wei was also making his first start for Celtic and he was out-muscled by Tom Brighton early in the game.
The former Rangers youngster ran in to drill the ball under Boruc but referee Kenny Clark harshly ruled that Du Wei had been fouled.
Boruc then had to save well from a deflected Steve Masterton strike.
The underdogs were sharp in attack and Alex Williams found the net after an almighty scramble in the penalty area.
This time it was a linesman's flag that came to Celtic's rescue, although television replays showed that the striker was not offside.
Clyde did not let the decisions get them down and took a thoroughly deserved 33rd-minute lead when Malone's cross was missed by Boruc and Bryson stooped to head into an empty net.
Keane had a Celtic debut to forget
Celtic striker Shaun Maloney came close to an equaliser when he scurried away from the Clyde defence but his low, angled shot was saved by the legs of keeper Peter Cherrie.
Du Wei's disastrous afternoon continued when pulled down Brighton to concede a penalty only for Boruc to fling himself right to save O'Donnell's effort.
Amazingly, the hapless defender went unpunished for the offence.
But Clyde went further ahead in the 37th minute when O'Donnell's corner skimmed the head of Du Wei and Malone launched a wonderful volley high into the net.
Clyde continued their great form early in the second half, with Brighton and O'Donnell trying their luck from long range.
O'Donnell then stole in front of Adam Virgo, a replacement for Du Wei, to crash a header against the base of the post.
On the hour, Keane found Aiden McGeady with a great pass from distance but the youngster fluffed an awkward shot with only Cherrie to beat from the edge of the penalty area.
The hosts tired as the game went on and Celtic clawed a goal back through Zurawski after 82 minutes.
The Polish international latched on to a headed knock-down from Stephen McManus and shot past Cherrie from 20 yards.
Celtic launched a series of long balls forward in the closing stages but the home defence coped comfortably to secure a major upset.
Clyde: Cherrie, McGregor, Higgins, McKeown, Malone, Bryson (Bouadji 82), Masterton, O'Donnell, McGowan, Williams (Miller 81), Tom Brighton (Arbuckle 89). Subs Not Used: Hunter, Jarvie.
Goals: Bryson 32, Malone 36.
Celtic: Boruc, Telfer, Du (Virgo 45), McManus, Wallace (McGeady 55), Nakamura, Lennon, Keane, Pearson, Hartson (Zurawski 71), Maloney. Subs Not Used: Marshall, Lawson.
Booked: McManus. Goal: Zurawski 82.
Ref: K Clark