The Robins fell to a 5-1 defeat away to AFC Wimbledon in the Emirates FA Cup first round at the Cherry Red Records Stadium.
Rob Street added a consolation goal late on in front of the travelling fans on a tough day for the team.
“It’s a woeful and embarrassing performance,” said Robins manager Darrell Clarke post-match.
“Apologies to the fans that came and watched that, it’s nowhere near good enough.
“But at least in the changing room we are all in agreement that’s what it was.”
The game adopted a scrappy nature from the first whistle with neither side creating anything of note until James Tilley shot wide in the 18th minute.
The growing threat from the hosts told four minutes later as Omar Bugiel’s flick on released Ali Al Hamadi in behind the Robins defence and he slotted home with ease.
The Robins continued to struggle to find their feet in the game and despite a first half change, the host doubled their lead on the stroke of half time with Tilley running onto a ball forward and touching it past Luke Southwood.
More changes followed at the break but they were unable to alter the pattern of play as an Armani Little rattled the crossbar before Connor Lemonheigh-Evans spurned a golden opportunity from 15 yards.
A third goal followed with Tilley adding his second of the game with a well-placed volley into the bottom corner.
Substitute Josh Davison added a fourth nine minutes later as he swivelled in the box and his effort found a way in after a couple of deflections.
The Robins’ afternoon continued to worsen as Lemonheigh-Evans rifled a shot from the left edge of the penalty area into the far top corner.
Despite the scoreline, the Robins kept pushing for a goal of their own and found one in the 76th minute as the rebound from Nathan Butler-Oyedeji’s shot fell to Street who tapped into an empty net.
Another foray forward resulted in a penalty for the Robins as Aidan Keena was hauled down but the Irishman’s spot kick rebounded off the post before his follow up was disallowed after no other player made contact with the ball.
The hosts nearly added a sixth in injury time as Davison volleyed over.
AFC WIMBLEDON (4-2-3-1): Bass; Biler (Ogundere 86), Lewis, Pearce, Currie; Reeves (c), Little (Ball 86); Tilley (Jennings 90), Bugiel (Davison 62), Evans (Sasu 86); Al Hamadi. Subs not used: Tzanev (Gk), Brown, Lakin, Kalambayi.
CHELTENHAM TOWN (3-5-2): Southwood; Long (c), Davies, Freestone; J. Williams, Sercombe, Thompson (Pett 62), Adshead (Butler-Oyedeji 41), Ferry (Bevan 46) ; Lloyd (Street 46), Goodwin (Keena 62). Subs not used: Harris (Gk), Bradbury, Olayinka, Malcolm
REFEREE: A Young
ATTENDANCE: 4,975 (433 from Cheltenham)