Ernesto Valverde's troops barely created chances in the first half, but the Partenopei made several changes at half-time, and Barcelona pounced. Suarez scored twice, while Antoine Griezmann and Ousmane Dembele also got in on the action.
The Catalans had won the first friendly between the two sides, a close 2-1 win in Miami Gardens, Florida. Saturday's match took place in Ann Arbor, Michigan.
Barcelona will start their La Liga title defence on Friday against Athletic, and Valverde opted to start a strong team in this dress rehearsal:
Carles Alena got the nod in midfield ahead of Ivan Rakitic and Sergio Busquets, two players likely to start on Friday.
Serie A will start a week later, and Barcelona had the look of a team that is further along in their preparations than the Partenopei. Napoli threatened a little on the counter in the first 30 minutes, but the Blaugrana dominated possession with their passing.
The possession didn't lead to chances, however, and Alex Meret had nothing to do before the first water break. Griezmann did have a good look on goal, firing an effort wide.
The match came to life after the drinks break, with Dries Mertens having a shot blocked and Kostas Manolas just about holding off Dembele. The Frenchman was by far the biggest Catalan threat in the first half, but despite his best efforts, Napoli easily survived the first 45 minutes and could have taken a lead late through Fabian Ruiz, who couldn't convert after a corner.
The highlight of the half was not a chance, but this back-and-forth between Manolas and Suarez:
The Uruguayan got his revenge early in the second half, however, bagging the opener after 48 minutes. Suarez fired home a rebound after Griezmann's initial effort, but the latter appeared to be offside in the buildup.
Napoli had already made three substitutions at the time, and their quality noticeably dropped. Just minutes after the opener, Griezmann doubled the lead after an assist from Jordi Alba. The Frenchman appeared to be offside again, but the goal was allowed to stand.
The Blaugrana were unleashed at this point, and Suarez soon made it 3-0 with a neat finish, with Dembele providing the assist this time around.
The standout got his own name on the scoresheet after 63 minutes, although Jack J. Collins of Bleacher Report thought the midfielders were stealing the show:
Barcelona finally made some changes after the fourth goal, giving Napoli some time to breathe. The Italians had made five substitutions before Valverde made his first.
The changes sucked the life out of the contest, with the play reverting back to the standards of the first half.