Pete Russell's team were within touching distance of a team ranked 12 places above them in the world rankings until two goals late in the second period left them chasing the game.
And despite conceding two further efforts in the third, Sheffield Steelers' forward Jonathan Phillips believes there were plenty of positives to take with just a week left until their tournament opener against Germany in Kosice.
"Slovakia came at us hard in the opening stages but we rode that out and grew into the game the longer it went on," said the 36-year-old Steelers captain.
"I felt we fully deserved our goal and at that stage it was a one-goal game and we felt we were right in it. But they showed their class in the third period and took the game away from us."
Tomáš Zigo's deflected shot past Bowns at 9.33 broke the deficit and although Ben Lake and Robert Farmer forced saves from Marek Ciliak in the Slovakia goal, that is how it remained until the first break.
Robert Dowd and Brett Perlini both had shooting opportunities for GB but the next goal came at the other end when Montreal Canadiens' forward Tomas Tatar, who amassed 58 points in the 2018-19 NHL campaign, slotted home a rebound from close-range to make it 2-0 at 28.15.
A powerplay strike from Farmer at 34.39 made it a one-goal game as GB stepped up the pace, but two goals in under four minutes swung the game away from them again, the first coming at 35.51 from Matus Sukel before Róbert Lantosi made it 4-1 at 39.16 on the power play.
Perlini and Farmer both went close in forcing the puck home on the doorstep early in the third, but another power play strike - this time via Martin Marincin at 45.25 - ensured there was to be no way back for the visitors, who conceded a sixth when Adam Liska produced a smart finish at 48.49.
"We can take positives from that performance for sure," added Phillips. "We certainly now know the standards we are going to have to achieve at this tournament and it was great preparation for us."