Tottenham hit Celtic for six
Mauricio Pochettino's men were unbeaten on their three-match tour of the United States last month, and never looked in trouble against the Scottish Champions at the Helsinki Olympic Stadium.
The Premier League side were 2-0 up inside 15 minutes thanks to goals from Harry Kane and Roberto Soldado and, though Jamie Lindsay pulled a goal back, Lewis Holtby made it 3-1 before the break.
Spurs played at a slower tempo in the second half but Erik Lamela, Christian Eriksen and Emmanuel Adebayor completed the rout.
Celtic named a youthful side, with manager Ronny Deila no doubt keeping one eye on Wednesday's UEFA Champions League third qualifying second-leg tie with Legia Warsaw, which they trail 4-1 from the first leg.
And Deila's me were behind in the sixth minute when Tottenham scored from their first meaningful attack.
Andros Townsend jinked his way into the area and picked out Kane, who took one touch and lashed his shot into the top left-hand corner.
Spurs wasted little time in doubling their advantage, scoring again on 13 minutes. Soldado finished at the second time of asking after Holtby had collected a kind ricochet and burst into the box.
And the Spaniard went close to a second shortly after when he headed wide of the left-hand post.
After a lull in proceedings, Celtic halved the deficit on the stroke of half-time. Brad Friedel made a fine stop from Dylan McGeouch's deflected shot, but the Scot crossed to the back post and Lindsay's header was adjudged to have crossed the line despite Friedel's attempt to keep the effort out.
However, Tottenham quickly restored their two-goal lead, as Etienne Capoue's throughball found Holtby and he coolly slotted home.
It was one of Spurs' half-time substitutes that made it 4-1, as Lamela's 20-yard effort was deflected past the helpless Craig Gordon, before Eriksen got in on the act with a trademark curling free-kick with seven minutes remaining.
And there was still time for Adebayor to add his name to the scoresheet, the forward stroking home a last-minute penalty after Danny Rose had been felled in the area.
Celtic's misery was then compounded as Efe Ambrose was dismissed for a second bookable offence - his second dismissal in the space of four days, after he was sent off in Warsaw on Wednesday.