Warriors coach Andrew Webster has described his side's top-four finish as "unbelievable" after their 18-6 win over St George Illawarra locked them in for a double chance in the finals.

Writing another chapter in their redemption story after last year's 15th-place finish, the Warriors guaranteed at least one Australian side would face the challenging task of crossing the Tasman to face the New Zealand-based club in the play-offs.

A stifling defensive effort carried the third-placed Warriors to their seventh-straight win, although it came at a cost.

Five-eighth Luke Metcalf left Mount Smart Stadium on Friday night clutching his hamstring in what could prove a huge blow just a fortnight from the finals.

Metcalf's absence did not help a Warriors side that lacked attacking creativity. They were held try-less for 55 minutes after two early scores before a late four-pointer sealed the win.

Webster said his side's stellar defensive showing separated it from other scrappy wins they have had in recent weeks.

"The boys defended unbelievably tonight, that was the best part of their game," he said.

"They [Dragons] scored a try from a kick, not from breaking us down, and I never felt like they really looked like doing that.

"Top four is an unbelievable achievement for the club, the whole club should be really proud. But we go to another goal now."

Cowboys remain in finals race

North Queensland coach Todd Payten said he was unsure whether Penrith counterpart Ivan Cleary would rest players or field a full-strength outfit when the two sides face off in the final round.

The Cowboys kept themselves in finals contention with a 34-10 victory over the Dolphins in Brisbane on Friday night.

They are ninth on 30 points, trailing the eighth-placed Rabbitohs – who have the bye this round — via an inferior for-and-against figure.