Connacht recovered from a 10-0 deficit to make it three wins in a row as Tiernan O’Halloran and Tom Farrell both touched down in front of a raucous home crowd at the Sportsground.
Jack Carty kicked two penalties and a conversion with Craig Ronaldson also kicking a conversion on a memorable night in Galway.
Connacht fell behind after four minutes as Rory Scannell offloaded for Simon Zebo to touch down under the posts after a fast and furious start.
Keatley added the conversion and the hosts were punished once again by the out-half on 16 minutes as he landed a straightforward penalty after Connacht infringed at the breakdown.
A high tackle on Ultan Dillane then gave Connacht the opportunity to get off the mark but Jack Carty pulled a tricky effort just left.
Connacht were back in it on 22 minutes as O’Halloran touched down under the posts on 22 minutes. Bundee Aki released Jarrad Butler with a brilliantly disguised pass down the left wing and the flanker sent O’Halloran away in the left corner as Carty’s conversion made it 19-7 after 22 minutes.
It was no more than they deserved and the hosts really had the bit between their teeth as Munster were forced onto the back foot.
The visitors quickly bounced back however and a second Keatley penalty on the half hour after Connacht were again pinged at the breakdown moved Munster 13-7 in front.
That penalty again spurred Connacht into action and O’Halloran, who was playing out of his skin, then won a five-metre scrum as his chip through was carried over by Keatley.
A scrum penalty ensued and Carty obliged with a well-struck penalty to make it 13-10 just before the break.
Connacht were in the ascendancy after the interval and were unfortunate to see Aki’s forward pass halt a promising move as he looked to send Cian Kelleher clear.
Another scrum penalty for Connacht on 50 minutes gave Carty a chance to level the scores and he made no mistake to move the scorebaord to 13-all.
Niyi Adeolokun came off the bench on his return from injury to rapturous applause as the Connacht scrum held firm to win a vital penalty deep in their own territory.
A red card for Andrew Conway on 61 minutes gave Connacht a huge boost as the winger caught Carty with an elbow as the out-half looked to chase his own chip.
Munster struck for the next score though as replacement JJ Hanrahan kicked his first penalty on 66 minutes after Connacht went off their feet.
The reply was swift and superb as Tom Farrell picked a superb line and Marmion timed his pass perfectly to send the centre over from 40 metres for a try that the Sportsground faithful will remember for a long, long time.
Replacement Craig Ronaldson converted and Connacht led 20-16 with 67 minutes gone.
Munster tried to fight their way back into the game but the Connacht defence was outstanding for the final 13 minutes as their provincial rivals didn’t get a sniff and Kieran Keane’s side made it three wins in a row.
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