The Argentina captain once again stole the show on his 100th European appearance as his late double set Barca on their way to victory at Camp Nou, before he provided the assist for Neymar's goal well into stoppage time.
The 27-year-old 's performance ruined the homecoming of Bayern coach Pep Guardiola, but the attacker has admitted things could easily have gone differently, before warning that the Bundesliga champions still pose a threat in next week's return leg at the Allianz Arena.
"We were lucky to score the first goal," Messi told reporters.
"Then the others came after that in quick succession and we have come away with a great result for the second-leg game, which is just what we wanted.
"Germany will be a tough venue. We have got a great result, but we must now go there and we can't drop our guard."
The forward then went on to explain that his jubilant celebration after his first goal was a result of Barca finally finding a way past Bayern.
"It was just my happiness about what the goal meant. We hadn't been able to score and it was an important goal in the tie."