Messi gave a tearful farewell to Barca at a news conference on Sunday after it was confirmed this week the forward's 21-year association with the club has come to an end.
The six-time Ballon d'Or winner's name was chanted by home supporters throughout the prestige pre-season match with Juve, who included Cristiano Ronaldo in their starting line-up.
Memphis Depay gave Barca the lead after three minutes and Martin Braithwaite added a second before the hour mark as Ronald Koeman's men rounded off pre-season with a win, with Riqui Puig scoring a fine third with the last kick of the contest.
New signings Yusuf Demir and Depay linked up for Barca's early opener, with the latter taking a throughball in his stride and picking his spot past Wojciech Szczesny.
That was Depay's third goal in four games since arriving from Lyon on a free transfer and he nearly had a second soon after when bending a free-kick narrowly over the crossbar.
Ronaldo was kept largely quiet during his 45 minutes on the pitch but did test Neto with a vicious shot in the first half, while Alvaro Morata was twice denied by the Barca keeper.
The hosts had some breathing space 12 minutes into the second period as Braithwaite's header from a Depay corner squirmed through the grasp of substitute keeper Mattia Perin.
Barca added a third goal to their tally in the final seconds through young midfielder Puig's curled effort from 20 yards to give Koeman hope of a bright future without club legend Messi.
The Blaugrana ran riot in their traditional Camp Nou curtain-raiser, with goals from Pedri (two), Lewandowski, Ousmane Dembele, Pierre-Emerick Aubameyang and Frenkie de Jong condemning the Mexican side to a crushing loss.
Barca took just 20 minutes to establish a 4-0 lead as Pedri scored twice after laying on new signing Lewandowski's opener, with the Poland striker returning the favour to tee up the skilful midfielder's second strike.
Lewandowski – who scored 50 goals in all competitions during his final season with Bundesliga champions Bayern Munich last term – was named as man of the match, leading Pedri to shower him with praise.
"It was important for us to win in front of our fans and we have achieved it by playing a good game," the midfielder said.
"The coach asks us all to reach the top and that we score goals, and I hope it continues like this. We've had a good pre-season and we wanted to start scoring soon.
"It is a luxury to play with Lewandowski, I really enjoy seeing how he finishes and how he links up.
"The president [Joan Laporta] and everyone have done a great job, and we will fight until May for it to be a very beautiful year for us all."
With Lewandowski joining Franck Kessie, Andreas Christensen, Jules Kounde and Raphinha in moving to Camp Nou ahead of the 2022-23 season, hopes are high that Barca can challenge for silverware – even if speculation persists that they may be unable to register their newcomers.
For Xavi, the performance against Pumas – for whom Barca legend Dani Alves featured – represented the standard the Catalan giants must hit in every match.
"Everything went well tonight, I'm very happy with the good game and for the fans, who have been excited. This is the way," Xavi declared.
"We are in a good dynamic of play and results, but we have to continue working for this to work. The sensations are good, yes, but there is no need to lower the pace or the intensity during the 90 minutes.
"Today it is understood that we relaxed a bit because we were 4-0 very early and it was a friendly, but in official competition you cannot lower your guard."
Barca begin their LaLiga campaign at home to Rayo Vallecano next Saturday.
