Martin O'Neill achieved his finest result in management as Celtic kept Barcelona at bay in the intimidating Nou Camp to reach the last eight of the UEFA Cup.
But O'Neill owes a huge debt to 19-year-old goalkeeper David Marshall who made a string of breathtaking saves to take Celtic through on aggregate.
It was a backs-to-the-wall display but ended with arguably Celtic's greatest result since they beat all-conquering Leeds United in the European Cup semi-finals in 1970.
Marshall took his place in goal in place of the suspended Robert Douglas and the 19-year-old did not have much time to settle.
Within the first minute, Ronaldinho sent Gerard clear but the goalkeeper managed to get his hand to the ball as the midfielder attempted to round him.
Celtic looked nervous in the opening minutes and Marshall had to be on his toes again to block a Gerard header after another Ronaldinho ball into the area.
Barcelona came close again from their first corner after 13 minutes when a close-in shot from Luis Enrique brought an instinctive save from Marshall.
The Catalans felt they should have had a penalty in the 21st minute when Ronaldinho tumbled in the area after a challenge from John Kennedy but Italian referee Domenico Messina waved away the claims.
Barcelona had the lion's share of possession and a netbound Oleguer shot struck Stanislav Varga as Celtic had another narrow escape.
Chris Sutton tried a speculative effort at the other end but he hooked his 25-yard shot well over the top.
Henrik Larrson gave Celtic some hope when his cross troubled Victor Valdes but the goalkeeper grabbed the ball at the second attempt with Alan Thompson bearing down on him.
Celtic lost skipper Jackie McNamara through injury six minutes into the second half and Manchester United-bound Liam Miller took his place.
Barcelona continued to set the pace and Luis Garcia curled a shot just a foot wide from the edge of the penalty box with half-an-hour left.
Larsson had Celtic's first shot on target in the 62nd minute after great work from Stilian Petrov but the Swede directed his effort directly at Valdes.
Marshall came to Celtic's rescue again when he blocked Ronaldinho's angled shot after the Brazilian had waltzed past four defenders.
But the young goalkeeper excelled himself when he tipped a Luis Garcia shot over the top with a world-class save when it finally seemed certain Barcelona would take the lead.
Marshall produced another incredible save to deny substitute Sergio with 15 minutes left.
But Celtic held on for a memorable result.