The winger's well-taken low finish after 15 minutes was all that separated the sides at St. James' Park, with William Osula being denied a debut goal for the Magpies after his goal was disallowed for offside.
Eddie Howe's side's victory meant they retained the Sela Cup for a second successive year, with Newcastle United Women also lifting their trophy after full time following their penalty shoot-out success over AC Milan Women earlier in the day.
United were totally dominant in a high-tempo first half. Osula saw an early angled drive saved by Marco Bizot in the Brest goal, Miguel Almirón rolled a shot just past the post and Barnes headed wide in what was a fast start from the hosts.
The breakthrough came after quarter of an hour. Defender Lloyd Kelly – on his first appearance at St. James’ Park since joining in July – played it long over the top for Barnes to collect on the left flank. He still had a lot to do, though, but did it superbly, cutting inside and keeping his balance before curling home low into the bottom right-hand corner.
Joe Willock then saw a mishit effort blocked by Bizot's legs and Bruno Guimarães nodded over before the Magpies thought they had gone 2-0 up. It was a smart finish from Osula, who sorted his feet out quickly after racing on to Barnes' through ball and finishing well, but he was denied a first for the club by the offside flag.
Brest offered little going forward, apart from Mathias Pereira Lage’s wayward hooked attempt and a Jordan Amavi drive which Martin Dúbravka palmed away, and after the break the hosts continued to press. Trevan Sanusi, impressive off the bench in the 4-0 win over Girona on Friday night, was brought on by Howe again and the tricky youngster immediately made his presence felt, beating his man and looking to play in Miguel Almirón, but the pass had just a little too much on it.
Sanusi was a threat down the left and it was his cross which led to Newcastle's next attempt, a sliced effort from Trippier that flashed past the post. The only real scare United had was a low cross from the right which Jeremy Le Douaron just failed to connect with, sliding in as it was fired across the face of substitute Odysseas Vlachodimos’ goal.
Greek goalkeeper Vlachodimos, another player making his home debut after signing in the summer, saved comfortably from Pereira Lage's header inside the final quarter of an hour, which was as close as either side got to finding the target late on as Howe’s men rounded off pre-season with another win.
Newcastle United: Martin Dúbravka (Odysseas Vlachodimos 46); Kieran Trippier (Harrison Ashby 68), Fabian Schär (Ellis Stanton 82), Lloyd Kelly, Jamal Lewis; Alfie Harrison (Trevan Sanusi 46), Bruno Guimarães, Joe Willock (Anthony Munda 88); Miguel Almirón, William Osula (Travis Hernes 68), Harvey Barnes.
Subs not used: Mark Gillespie, Leo Shahar, Cathal Heffernan, Johnny Emerson.
