St George Illawarra slumped to their third loss in a row at Suncorp Stadium after leading the Warriors 18-6 at half time
The Dragons' Saturday night Magic Round game ended in a disappointing and disappearing act.
The Warriors' scored 20 straight points after half-time was in the same vein as Parramatta's 32-18 come-from-behind win over McGregor's team last week.
"In the second half we stopped working in defence, all the things we did well in the first 40 minutes we didn't continue to do," McGregor said after the 26-18 loss.
"You need to be a consistent side for 80 minutes in this competition."
The body language of players after conceding late points over the past fortnight will be a worry for coach McGregor.
The loss against the Warriors drops the Dragons to 10th place on the NRL ladder.
Like the Sharks, their NRL neighbours who are just finding a way to win, the Dragons are missing experienced players and are being mowed down by opposition sides.
A fractured cheekbone is keeping Corey Norman out for at least another two weeks, Gareth Widdop permanently on the sideline and Jack de Belin is suspended under the NRL's no fault stand down policy.
While the Warriors Kodi Nikorima enjoyed a happy homecoming to Brisbane, it wasn't like that for fellow former Bronco Ben Hunt.
In a cruel repeat of his infamous knock on in the 2015 grand final, Hunt fumbled a 69th-minute dropout that swung the dying stages the Warriors' way.
St George Illawarra can also expect to be without players Ben Hunt, Paul Vaughan, Tyson Frizell and Tariq Sims when the Origin rolls around in a month's time, hastening McGregor's search for answers to their worrying second-half defensive dramas.
"It's not good enough McGregor said.
"We have to look at why it's happening and address it quickly."
The Dragons play Newcastle at Mudgee in their round 10 NRL clash next Sunday at 2pm.