It was the first of a couple of good team tries by the Sea Eagles, Williams again in the action in the 46th minute, finishing off another play that started with a line break by debutant halfback Peta Hiku and passed through three more sets of Manly hands.
That try came minutes after the Cowboys had grabbed the lead back through pivot Michael Morgan, who took advantage of a bad bounce on Manly fullback Brett Stewart and scored his own grubber kick on 42 minutes.
But that was the last piece of joy for the Cowboys, as the Sea Eagles ran in three more tries over some lacklustre Cowboys defence.
Jorge Taufua, Justin Horo and Steve Matai made it look easy as they crossed the line in the final half-hour to hand the Townsville team their second straight loss.
With back-to-back wins a rarity in the past 10 weeks, Sea Eagles captain Jamie Lyon said it was a record the players were keen to amend.
"We knew we had to get a couple of wins and we've struggled the previous few weeks so it was good to finally get two wins in a row and get a couple of points," he said.
Cowboys coach Neil Henry said his side had been hurt by their inability to defend errors in their own half.
"We were in the mix at half-time and the second they blew us away really," Henry said.
"I don't think they made an error, they were at one stage 17 of 17 (completed sets) and we made six errors in the second half.
"We needed to play some footy and unfortunately we didn't and gave up some field position."
- AAP