An injury-time equaliser from Jan Vennegoor of Hesselink kept Celtic's Scottish Cup hopes alive at Aberdeen on Sunday.
The Dons had looked set to pull off a shock win when an excellent goal from Jeffrey De Visscher gave them the lead with 11 minutes to go.
But Vennegoor of Hesselink stabbed home from close range in the dying seconds to earn the Bhoys a replay at Parkhead.
Celtic rattled the woodwork twice in the first half - via Scott McDonald and Vennegoor of Hesselink.
However famous home win looked on the cards when De Visscher exchanged a series of passes on the edge of the box with Lee Miller before firing home.
Only a couple of good saves from Artur Boruc kept Celtic in the game, while at the other end Gordon Strachan's side hit the post for the third time - Paul Hartley rattling the upright from long range.
However, Celtic did pull level in the first minute of added time when Vennegoor of Hesselink prodded in a tempting low cross from substitute Georgios Samaras to leave Dons boss Jimmy Calderwood with his head in his hands.
The eventual winners will meet First Division Queen of the South in the semi-finals.
Celtic's arch rivals Rangers remain in the hunt too after they saw off Hibernian 1-0 in their fifth-round replay at Ibrox.
Chris Burke fired the Gers into the last eight when he bagged the only goal of the game shortly before the break.
Burke collected a Steven Davis pass from the left before squeezing his shot between two green jerseys, leaving Yves Ma-Kalambay with no chance as the ball nestled in the right-hand bottom corner.
Steven Naismith also hit the underside of the bar with a close-range header but Rangers could not finish off their dogged opponents.
The tie erupted in the final minutes when substitute Nacho Novo was red-carded for a two-footed tackle on Thierry Gathuessi and boss Walter Smith was sent to the stand.
However, the hosts held on with 10 men to secure a home tie against First Division outfit Partick Thistle in the quarter-finals on March 19.
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