Monaco produced one of the all-time European upsets when they overcame a 4-2 first-leg deficit to knock Real Madrid out of the Champions League with a 3-1 victory in the second leg of their quarter-final on Tuesday.
Inspirational captain Ludovic Giuly scored twice as the French league leaders recovered from a goal down on the night to level the aggregate score at 5-5 and qualify for the last four on the away goals rule.
In the semi-finals they will meet Chelsea, who also came from a goal down on the night to beat London rivals Arsenal 2-1 at Highbury and advance 3-2 on aggregate thanks to a goal three minutes from time by defender Wayne Bridge.
First Win
It was Chelsea's first win in 18 attempts against Arsenal, whose treble dreams are in tatters after they were also knocked out of the FA Cup semi-finals by Manchester United on Saturday.
Monaco, trailing by two goals from the first leg in Spain, looked down and out when Raul gave nine-times champions Real a 36th-minute lead.
Giuly gave the principality side hope with a goal on the stroke of halftime, though, before Spain striker Fernando Morientes, on loan from Real, made it 2-1 after the break.
Giuly's deft 66th-minute flick sealed the win and Monaco even hit the woodwork twice in the closing stages.
"The players are writing a beautiful page of the club's history and also of French football history," said Monaco coach Didier Deschamps. "It's an outstanding achievement."
Real's dejected midfielder Zinedine Zidane graciously said: "The best team won tonight, we're all very disappointed."
In London, Arsenal had the best of the first half and deservedly took the lead in injury time with a close-range shot by Spanish striker Jose Antonio Reyes.
It was the first goal Chelsea had conceded in six European away games this season and, having not won a meaningful game at Highbury since 1990, the odds swung heavily in Arsenal's favour.
But Chelsea equalised six minutes into the second half when goalkeeper Jens Lehmann failed to hold a swerving Claude Makelele shot and Frank Lampard swept in the rebound.
Arsenal defender Ashley Cole cleared an Eidur Gudjohnsen shot off the line five minutes from time but two minutes later the Icelander played a perfect return pass into the path of fullback Bridge who drove in the winner.
"When they cleared that shot off the line I thought it wasn't going to be our day," Bridge told ITV.
"But we battled, matched them for effort. It was a great ball from Eidur and I just sidefooted it into the corner."
Manager Claudio Ranieri said: "Fantastic, the players delivered.
"It was important to stay calm. I said 'don't worry, we can score' and the second half was a great performance."
In the last four Monaco will be at home to Chelsea in the first leg on April 20 with the return in London on May 5.
Holders AC Milan are heavily favoured to join them in the last four as they visit Deportivo Coruna on Wednesday with a 4-1 lead.
