Haaland netted twice late in the first half of the quarter-final at the Etihad Stadium and completed his treble after the interval following an Antoine Semenyo strike.
With Liverpool trailing by four, Mohamed Salah had a penalty saved by City goalkeeper James Trafford to compound a miserable afternoon for the under-fire Slot.
Liverpool head to Paris Saint-Germain for the Champions League quarter-final first leg on Wednesday with Slot desperately needing a victory over the holders to keep the critics at bay.
“We have had a lot of setbacks and disappointments but that is also part of being a football player and being a human being. You have to stand there when things are not so positive,” Slot said.
Liverpool, who have just two wins in their last seven matches in all competitions, are fifth in the Premier League and far from certain to qualify for next season’s Champions League.
City’s ruthless performance took them into the FA Cup semi-finals for an eighth successive season.
After beating Liverpool twice in the Premier League this term, City have enjoyed three successive victories over the Reds for the first time since 1937. (AFP)
Edited by Tony Sabine
