And reigning All-Ireland clubchampions Clarinbridge came from three points down to go ahead in injury-time only for Mullagh to equalise in the dying seconds of their last eight clash.
Portumna, who had only lost three of their previous 41 championship games in Galway, were ousted by a St Thomas side in a gripping contest at Ballinasloe.
A goal just before half-time from Galway inter-county midfielder David Burke proved crucial for St Thomas who reached their first countysemi-final in 22 years.
Playing without Joe Canning and Andy Smith who were suspended after picking up red cards in their final group match against Athenry,Portumna looked like taking a one-point lead into the break after Niall Hayes was on target.
But David Burke had different intentions — he pulled on a long delivery from Enda Tannian which flew to back of the Portumna net. That goal fired St Thomas to a 1-6 to 0-7 half-time lead.
However, Portumna, who were playing with a strong wind in the second-half, were still expected to power past their youthful opponents and the accuracy of Davy Canning from dead balls was keeping them in touch.
However with time running out, Galway U21 forward James Regan came to the fore with three points in the final eight minutes — he hit five in total — which saw them progress into the last four (1-10 to 0-12).
All-Ireland champions Clarinbridge got out of jail with three late points to force a replay against Mullagh in Athenry.
A goal after four minutes from Paul Coen gave the champions a 1-6 to 0-4 lead, but a storming start to the second-half saw Pete Finnerty’s Mullagh lead by a point with seven minutes remaining.
Points from Davy Glennon and Finian Coone looked to have Clarinbridge dead and buried, but a score from Coen and two Mark Kerins frees saw the latter now look set for victory, only for Coone to clinch a deserved draw for Mullagh with the last puck of the game.
Goals from Ollie Fahy and Keith Killilea saw Mattie Murphy’s Gort also reach the semi-finals as they ousted last year’s losing finalists Loughrea.
Gort held an 0-8 to 0-7 lead at half-time, with six points from Gerry Quinn.
Richie Cummins stretched their advantage to two points after the restart, and Fahy’s goal put them well in control. However, a goal from a Johnny Maher free at the other end just reduced the deficit for Loughrea but Killilea killed off their challenge in injury-time.
Craughwell, who won the last of their five Galway SHC titles in 1931, are also into the semi-final after a deserved 0-19 to 0-11 victory over Carnmore. The latter, who had the only 100% record in this year’schampionship, were favourites to claim the win in Athenry on Saturday, but a late charge from Craughwell proved their undoing.