The Warriors inflicted a fourth successive defeat on the North Queensland Cowboys with a 22-12 victory at Mt Smart Stadium on Saturday.
David Fusitu'a ran in two first-half tries for the Warriors as they led throughout against the battling Cowboys, whose only win was in round one against Cronulla after reaching the 2017 grand final from eighth spot.
The Cowboys are third last in star player Johnathan Thurston's final season.
The Dragons held off a late South Sydney surge to win 16-12 at Jubilee Oval on Friday night and join the Warriors with five straight wins to start the season.
St George Illawarra led 16-6 with eight minutes to play, but a Cody Walker try for the Rabbitohs set up a thrilling finish.
Wests Tigers also continued their unexpectedly strong start to the season with their fourth win, at the expense of the Melbourne Storm on Saturday.
The Tigers won 11-10 to leave the Storm with just two wins from five matches and sitting outside the top eight.
A Benji Marshall field goal in the 75th minute won the match for the Tigers.
Newcastle continued their good start to the season with a 15-10 win over a disappointing Brisbane on Saturday to notch their third victory.
Parramatta had been tipped as one of the sides to beat this season. But they have lost their first five games for the first time in 27 years after being beaten 12-6 by Penrith in the round's final game on Sunday.
It was the fourth win for the Panthers who are in the top four, while the Eels are the only winless team.
The round started with Canberra finally breaking their drought for 2018 after several narrow losses with a 26-10 win over Canterbury on Thursday.
In other results, Sydney beat Cronulla 28-10 and Gold Coast downed Manly 32-20.