St George Illawarra's hopes of squeezing into the NRL finals have taken a huge hit after their controversial loss to Canterbury at Accor Stadium.

The Dragons looked like they were about to cause a boilover win over the high-flying Bulldogs but a late try to Jethro Rinakama with less than three minutes on the clock gave the home side a 20-18 triumph.

Dragons coach Shane Flanagan was irate over two calls from the match officials which he said cost his team the two valuable competition points.

"I was really proud of the effort they put in and the way they played, but the game was taken away from us from I believe wrong decisions," he said.

He was particularly incensed after Canterbury successfully used a captain's challenge for a call on Jacob Kiraz, who planted the ball illegally as Luciano Leilua was ruled to have interfered in the ruck.

Flanagan described that decision as "outrageous".

"He's got to get to his feet before he plants the ball. You can't be falling sideways. You can't ball-plant. We lost the game because of it."

Flanagan was also angry over Viliame Kikau batting the ball into Tyrell Sloan as he tried a quick pass on the left edge but the call was missed in the lead-up to new halfback Lachlan Galvin throwing the pass to Rinakama a short time later.

"In the collision that's a knock-on. Ever since 100 years, that's a knock-on and that was at the 78-minute mark," he said.

'Some decisions tonight cost us two competition points and could cost us an opportunity to play semi-finals."

The Dragons have now lost eight matches this year by 10 points or less.

Kiraz scored the first try of the match but Sloan countered in the 16th minute.

Galvin and Reed Mahoney crossed to make it 16-8 at half-time but St George Illawarra rallied with centre Moses Suli and winger Sione Finau getting on the scoresheet to put the underdogs up with 25 minutes remaining.

They hung on grimly as the Dogs kept hammering their line before finally breaking in the 78th minute for Canterbury to rise into second spot following Melbourne's surprise home loss to Manly.

Gerringong Lions forward Hamish Stewart made 27 tackles in just 32 minutes along with 67 metres from eight hit-ups.

The Dragons are 11th with a 6-11 record, likely needing to win their final seven matches to get a spot in the playoffs.

In the NRLW, the Dragons rose to a 2-1 record for the season after sinking the Dogs 18-14.