Highfield 36 Dolphin 0, Woodleigh Park
Shannon 22 Garryowen 16, Coonagh
Sunday's Well 20 Old Crescent 17, Musgrave Park
UL Bohemians 20 Cork Constitution 21, Annacotty
Having gone behind for the first time midway through the second half, Shannon battled through to the last-four with two penalties from Andrew Thompson and an injury-time drop goal from Pat O'Connor sealing the victory.
Garryowen, who claimed four major trophies last season including the Munster Senior Cup, were trailing by the tenth-minute when Shannon winger Andrew Finn, helped by the good of the hosts' pack, crossed for the game's opening try which Thompson converted.
The visitors, who had the backing of the wind in the first half, hit back when out-half Alan Kingsley won the race to touch down his side's first try in the 17th-minute.
That score went unconverted and two penalties from the boot of Thompson, who played alongside John Clogan in Shannon's midfield, to one at the other end from Conor Kilroy had Mick Galwey's men 13-8 in front at the break.
Ten minutes into the second half, Garryowen grabbed an unconverted try to get back level. Team captain Paul Neville was involved in the build-up before centre Conan Doyle was released for a well-taken score.
The defending champions edged into front soon after, when Kilroy slotted his second penalty but Shannon, using their wind advantage well, had much the better finish.
Their path through to the semi-finals was completed as two lovely penalty strikes from Thompson on 54 and 64 minutes were followed by a drop goal from winger O'Connor, who bisected the posts five minutes into injury-time.
Afterwards, Shannon coach Galwey was quick to praise the likes of Clogan, hooker Sean Cronin, lock Fergal Walsh and flanker Leonard Mullane, who was playing in his first senior game for the club.
Best for Garryowen on the day were flanker Neville, Ireland "A" winger Keith Earls and busy scrum half Gerry Hurley.
Shannon's opponents in the November 24 semi-final will be Cork Constitution as the Leesiders, despite losing Munster's Jeremy Manning to injury, overcame UL Bohemians 21-20 in a thrilling game at Annacotty.
Another of Munster's back-line talents, Barry Murphy, had a superb game in the centre for Bohs. His 35-metre run yielded one of the hosts' tries for their former captain Colman Finn.
But the Limerick side left themselves with too much to do when they conceded three tries in the opening 20 minutes, with Con's Daniel Nethery, Ed Leamy and Richie Lane crossing the whitewash and Manning converting all three efforts.
Tries from Bohs' new skipper Martin McPhail, Tommy O'Donnell and Finn, allied to five points from the boot of Aidan McNulty, had the deficit cut to a single point by the 55th-minute but the scores frustratingly dried up for Ian Costello's charges in the final quarter.
The other semi-final in November will be an all-Cork affair after Highfield and Sunday's Well won their respective matches on Saturday. Highfield had an excellent 36-0 win over Division One outfit Dolpin at Woodleigh Park.
Coached this season by former Shannon and Buccaneers boss Geoff Moylan, Highfield were 17-0 in front at the break thanks to tries from Conor O'Leary, John Gleeson and prop and captain Dave Ryan.
Dolphin simply had no answer to the hosts' power and pace and further tries for O'Leary and Conor Mahony (2) saw Moylan's men confidently through to the last-four.
Sunday's Well overcame a late surge from Old Crescent to win their quarter-final tie 20-17 at Musgrave Park on Saturday. Helped by a strong showing from their pack, 'Well had to come from behind as Crescent's Welsh out-half Gareth James put them in front courtesy of a ninth-minute try.
But that proved to be the visitors' only score of the first half as Well impressively took over. Centre John Lynch kicked a 13th-minute penalty goal for them and out-half Tilla Toaliloa muscled over for a converted try, some 13 minutes later.
An excellent maul from the 'Well forwards finished with back rower Jason Rose crossing the whitewash to leave his side 15-5 to the good at half-time.
That lead was strengthened in the 68th-minute when Lynch was on the end of a flowing move to grab 'Well's third try, and the Division Three team were well on the way to defeating their Division Two opponents.
Mark Ring's Crescent side charged forward to notch two late tries through scrum half Alan Purcell and full-back Brian Begley, but it was not enough to deny the Ian Carroll- captained victors.