At the half-hour mark, the 31-year-old captain found the upper right-hand corner to give Barcelona the lead in its Champions League opener.
The first goal of the 2018-19 Champions League group stage was a stunner from one of the all-time greats.
Lionel Messi gave Barcelona a 1–0 lead over PSV Eindhoven with a spectacular free kick on Tuesday in the teams' opening match in Group B play.
At the half-hour mark, the 31-year-old captain found the upper right-hand corner from about 25 yards out, as PSV goalkeeper Jeroen Zoet helplessly tried to stop it despite his acrobatic attempt.
That goal was the only score for much of the match, until the 74th minute when Barcelona began to pour it on.
It started with Dembele launching a shot from outside the box.
Then, in the 77th minute, Messi found the back of the net once more to push Barcelona's lead to 3-0.
And in the 87th minute, Messi completed the hat trick with another wonderful goal to make it 4-0.
Barcelona and PSV are in a tough group, with Inter Milan and Tottenham rounding out what many consider to be this season's group of death.
Messi will be looking to help lead Barcelona to its first Champions League title since 2015. Last year, Barcelona's rival, Real Madrid, captured its third straight Champions League title and fourth in five seasons.