If it was Barca's team play that ripped Arsenal to shreds in the first hour of last week's first leg, which ended 2-2, it was Messi's sublime talent that propelled Pep Guardiola's side to a 6-3 aggregate victory and set up a clash with Jose Mourinho's Inter Milan.
The Londoners nosed ahead through Nicklas Bendtner in the 18th minute but from then on it was all about Messi, who produced goals of sheer class in the 21st, 37th and 42nd minutes to all but kill off the visitors' hopes.
With two minutes of regular time remaining, the 22-year-old FIFA World Player of the Year completed his virtuoso display after pouncing on a rebound to drill the ball through the legs of Arsenal goalkeeper Manuel Almunia.
NEWS:Messi 4-1 Arsenal
The stunning haul took his tally in the competition to eight, putting him top of the scoring chart ahead of Real Madrid forward Cristiano Ronaldo, and added to his 26 La Liga goals this season.
"We started badly but ended in spectacular fashion," a euphoric Messi told Spanish television. "I am very pleased but the important thing is that the team keeps winning."
COOL FINISH
Barca seized early control of possession at a packed Nou Camp and Messi tested Almunia with a fierce drive in the fourth minute and sent a curling strike whistling just over the crossbar shortly after.
It was a sign of things to come but the visitors silenced the home fans with a breakaway goal.
Abou Diaby robbed Gabriel Milito in midfield and as the Barca players appealed for a foul Theo Walcott raced clear on the right and set Dane Bendtner up to score at the second attempt past Victor Valdes.
The goal seemed to fire Barca into action and they were level within three minutes when Messi picked up a loose ball on the edge of the area and lashed a shot through a crowd of defenders into the top corner.
He made no mistake with a cool finish high into the net from close range after Pedro's smart layoff to put Barca ahead on the night and his third goal shortly after was the pick of the four.
Seydou Keita nodded the ball into his path, catching the Arsenal defence flatfooted, and as Almunia advanced to meet him Messi scooped the ball over the Spaniard and into the empty net.
Arsenal made a better fist of things in the second half, enjoying more of the ball in the central areas, but rarely threatened the Barca goal and Pedro went close in the 72nd with a chipped effort that flew just wide.
As Arsenal tired, Messi struck again in the 88th, twisting one way and another through the defence before beating Almunia for a fourth time.
ECSTATIC FAITHFUL
"Yes yes yes - we're going to Madrid!" roared the fans in reference both to May's final at the Bernabeu stadium of Barca's arch rivals Real and Saturday's La Liga match between the p
