A resilient Blades defence was undone shortly before the break, Mahrez dispatching from the penalty spot after Daniel Jebbison's rash challenge on Bernardo Silva.

United's hopes of a second-half comeback were wiped away by the Algerian, with just six minutes separating his second and third efforts.

Mahrez's treble was the first FA Cup semi-final hat-trick at Wembley and the first at this stage overall in the competition since Alex Dawson for Manchester United against Fulham in 1958

Also through to the UEFA Champions League semi-finals and five points behind Arsenal, which is faces on Thursday (AEST), with a game in hand in the Premier League title race, City remains firmly in the hunt on three fronts.

The Blades had a glorious opportunity inside 90 seconds, John Egan flicking a header from a corner that found Iliman Ndiaye in space but he could only fire straight at Stefan Ortega.

Erling Haaland then had the ball in the back of the net after 15 minutes, smashing home from distance, but his celebrations were halted as the whistle had already blown for a foul, with Julian Alvarez then forcing a diving save from Wes Foderingham with his long-range curler.

An impressive defensive performance from the Championship side was undone four minutes before the break, Jebbison's clumsy challenge on Silva handing Mahrez an opportunity from the penalty spot, which he duly tucked into the bottom-right corner.

City's second came on the hour mark, Mahrez winning the ball at the halfway line from Max Lowe and marching straight through the Blades defence, which backed away and gifted him space to run into.

Mahrez completed his hat-trick six minutes later, firing home after Jack Grealish's cutback to put the result beyond any doubt and book City's spot in June's final.

Victory capped off what has been a stellar week for City, which progressed past Bayern Munich in the UEFA Champions League and saw title rival Arsenal slip up against Southampton in the Premier League.