PHILADELPHIA — It’s exactly two weeks before the season-opening showdown with the Miami Heat and the Celtics have shown little championship-caliber play in the preseason.

The Celtics were flat-out embarrassed Monday night at the Wells Fargo Center as the Philadelphia 76ers turned into the Harlem Globetrotters in the second half and coasted to a 107-75 exhibition victory, Boston’s third preseason loss.

The 76ers used a 24-4 run to open up a 27-point lead (90-63) as they seemingly took turns dunking on the Celtics’ nonexistent defense. Spencer Hawes led Philadelphia with 17 points and Nick Young added 14 in 23 minutes as the 76ers looked as if they were trying to send a message in showboating halfway through the fourth quarter.

While the Celtics don’t put much emphasis on preseason games, they weren’t competitive most of the second half, scoring 8 points in a 12-minute span between the third and fourth quarters. The Celtics trailed, 66-59, with 6:30 left in the third quarter and that deficit expanded to 104-69 with four minutes left in the game.

The Celtics are now 1-3 in the preseason. They make their TD Garden debut Tuesday against the Brooklyn Nets.

Two Celtics scored in double figures as they finished with 21 turnovers, 3-for-15 shooting from the 3-point line, and 38 percent shooting from the field.

Doc Rivers said he reads little into exhibition games but he couldn’t have been encouraged with the Celtics’ first-half performance. After drawing to within 36-35 on a Darko Milicic hook shot at the 6:27 mark of the second period, they were outscored, 20-7, for the remainder of the quarter and were careless offensively, committing seven turnovers in that span.

The interior defense was also porous, evidenced by 13 first-half points from Hawes on 4-for-7 shooting. He scored at will in stretches while third-string point guard Maalik Wayns added 8 points. The Celtics actually shot 45 percent in the first 24 minutes but missed all five 3-point attempts and committed several turnovers.

With Kevin Garnett getting the night off, the Celtics relied mainly on Paul Pierce, who led the Celtics with 16 points in 20 minutes. Brandon Bass added 11 points.