The Blues midfielder's tame 77th-minute spot-kick was easily saved by Donny goalkeeper Pontus Dahlberg as the visitors were forced to settle for a share of the spoils at the Keepmoat Stadium.
Danny Cowley's troops did at least make it four league matches unbeaten - without conceding - to start the season, although they were knocked off top spot - dropping third after the stalemate.
Pompey were fortunate not to find themselves a goal behind after 19 minutes. Tommy Rowe had his initial effort superbly saved by Gavin Bazunu before firing home the rebound, only for the linesman to flag for a foul following a slight push on Clark Robertson in the build-up.
The Blues were struggling to string attacks together and gifting possession back to Donny, with the hosts taking control.
Pompey then had Bazunu to thank for keeping things level as he was out quickly to stop former midfielder Ben Close's effort after being slipped through nine minutes before the break.
Substitute Michael Jacobs so nearly made the breakthrough for a Blues side who were a little brighter after the restart. His drilled effort from the edge of the area looked destined for the far corner but Dahlberg pulled off a fine stop after 67 minutes.
Dahlberg was the Donny saviour again as he superbly palmed away Marquis' point-bank header from the resulting corner.
The visitors were then gifted the chance to go ahead 13 minutes from the end when Gassan Ahadme was shoved to the ground in the area by Ro-Shaun Williams, with referee Carl Boyeson pointing to the spot.
However, substitute Shaun Williams' tame spot-kick was easily saved by Dahlberg down to his right.
Another substitute, Branden Horton, so nearly snatched the points yet Bazunu tipped his scuffed strike onto the crossbar with a minute left.