'We are going to miss him, but I am so pleased that he is in a position where he can leave having won trophies'
The west country club booked a seventh appearance in the competition’s last four and kept alive hopes of recapturing a trophy they last won 13 years ago by beating Recreation Ground visitors London Irish 26-13.
Bath have also been Challenge Cup runners-up three times, and they are now in a strong position to push for silverware once again.
“We are chuffed to bits to be in the semi-finals,” Bath rugby director Hooper said. “I am proud of the lads.
“We talked about finding a point of pressure and going after it tonight, and the boys did that well.
“It is a big win for us and to be in the semi-finals. These are the stages of competitions that we want to be in.”
Bath took charge of the all-Gallagher Premiership encounter through prop Will Stuart’s try double and a touchdown for their former Irish lock Josh McNally that underpinned a comfortable interval advantage.
Mercer will leave Bath to join fellow Challenge Cup quarter-finalists Montpellier next season, and Hooper added: “Zach was outstanding.
“We are going to miss him, but genuinely I am so pleased that he is playing well and in a position where he can leave this club having won trophies.”
Irish staged a stunning late fightback to defeat round of 16 opponents Cardiff Blues, yet there was no repeat seven days later.
They were in the contest until late on following hooker Agustin Creevy’s try, plus a Paddy Jackson conversion and two penalties, but Bath proved worthy winners.
Irish rugby director Declan Kidney said: “The little things just cost us a lot tonight, which happens in knockout rugby.
“We had an honest go at the competition, and it has been a great experience for our players.”
Bath are guaranteed to be joined by at least one other English club in the semi-finals, with Leicester hosting Newcastle on Saturday, while Northampton entertain Ulster and Montpellier tackle Benetton.
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