Rovers led at the Keepmoat Stadium courtesy of Charlie Seaman’s powerful opener less than a minute into the second half.
But Wellens’s disjointed team, which comprised 10 debutants, lost their way as the visitors battled back to claim a welcome win.
Ayoub Assal levelled with a close-range strike just before the hour-mark and there was still time for Luke McCormick, Wimbledon’s only debutant, to curl home a free-kick winner with 16 minutes remaining.
“That is the first time that 11 has played together,” admitted Wellens. “At times we did look like a team that was just made up.
“We looked really nervous, especially in the first half. Maybe that gave Wimbledon a bit more freedom to play. They were away first and it could have given them that. But the biggest disappointment from me is that we didn’t give the crowd enough to sing about and turn it into an atmosphere that it should have been on the opening day.”
Wellens revealed he had picked a different starting team but was forced to hastily shuffle his pack due to last-minute injuries.
“I picked a team on Thursday and then on Friday you’re having to change it because of injury concerns,” reflected Wellens. “But we’ll get better and we’ll improve. We need to do it quickly. We’re under no illusions that we’re in a tough league and we need to get it right quickly.”
Doncaster Rovers: Dahlberg, Knoyle, Williams, Anderson, Rowe, Smith, Close, Gardner (Bostock 60), Seaman, Cuker (Bogle 66), Barlow (John 66). Unused substitutes: Jones, Williams, Greaves, Horton.
AFC Wimbledon:Tzanev, Alexander, Heneghan, Nightingale, Guinness-Walker, Woodyard, Hartigan (Marsh 70), Rudoni, Assal, McCormick (Chislett 79), Palmer (Pressley 69).Unused substitutes: Lawrence, Csoka, Kalambyi, Oualah.
Referee: S Barrott (West Riding).