Willian hit the post twice but finally found the net with what looked to be the winning goal, only for Messi to score for the first time in six games to earn a 1-1 draw at Stamford Bridge on Wednesday, leaving the clash finely balanced.
Chelsea and Barca were facing each other for the 13th time in the Champions League, renewing their rivalry after a classic semi-final clash in 2012, and for much of the contest there was nothing between the sides despite Barca's inevitable dominance of the ball.
Barcelona had 75 per cent possession in the first half but the Catalans were perhaps fortunate to go into half-time level, Willian having been denied by the woodwork on two occasions.
He fine-tuned his radar after the interval, however, rifling home into Marc-Andre ter Stegen's bottom-left corner to give Chelsea the lead.
But Messi pounced on his only chance of the game, capitalising on sloppy Chelsea defending to slot in from Andres Iniesta's pass to give Barca a narrow advantage ahead of the second leg on March 14.
— OptaJoe (@OptaJoe) February 20, 2018
Eden Hazard, playing a central attacking role with Alvaro Morata and Olivier Giroud benched, flashed a drive over as Chelsea made a bright start.
Antonio Rudiger flicked Willian's right-wing corner wide, then Paulinho missed an even better aerial chance when picked out by Messi, planting his header wide of the post.
Ter Stegen made a comfortable save to keep out Willian's free-kick after the Brazilian had been brought down by Ivan Rakitic, who earned the game's first booking.
Willian was even closer with his next effort after 33 minutes but, although Ter Stegen was well beaten, the 25-yard curler cracked against the post and rebounded to safety.
And from an almost identical position Willian hit the woodwork again, this time clipping the outside of Ter Stegen's right-hand post with a strike that curled away from the goalkeeper.
Luis Suarez flashed a strike across goal as Barcelona built pressure, but they were caught out by the sucker punch as Willian finally found his range after 62 minutes.
IT HAD TO GO IN !!! willyyyyy @willianborges88
— Michy Batshuayi (@mbatshuayi) February 20, 2018
A short corner from the left was worked to Willian on the edge of the box and he used Rudiger as a shield to bend a superb strike into Ter Stegen's bottom-left corner.
Suarez had a strong penalty appeal rejected after Rudiger challenged the striker in the box, but Barca drew level with 15 minutes to play.
Andreas Christensen, preferred to captain Gary Cahill, gave the ball away on the edge of the Chelsea area, with Iniesta working the ball to Messi for a straightforward low finish.
Both sides thereafter appeared to settle for a draw, Christensen's lapse in concentration proving costly ahead of next month's second leg.
"Leo Messi has scored against Chelsea."
— FC Barcelona (@FCBarcelona) February 20, 2018
Photo Getty Images. Caption: Barcelona's Lionel Messi and Andres Iniesta celebrate