Niu scored twice in the first half before his third with 12 minutes to go looked to have put the result beyond doubt, only for Felise Kaufusi to then be sent to the sin bin for a late tackle which saw him put on report for the second time in the game at McDonald Jones Stadium.
It set up a nervous finish, before Isaako's double inside the last five minutes saw Wayne Bennett's side get past a stubborn Knights side who had three players appearing at NRL level for the first time, with a bench that had just 18 total games of first-grade experience.
The Dolphins controlled much of the first 40 minutes to lead 16-12 at the break, but couldn't shake the plucky Knights who were led by an inspired showing from fullback Lachlan Miller, who at one stage looked set to lift his team to victory after scoring five minutes either side of the break.
After the Dolphins fought back to lead 26-18 with 11 minutes to play, following the Knights hitting the front early in the second half, Newcastle centre Bradman Best blew a golden chance to put his side back into the game when he dropped a potential try over the line, and minutes later Isaako's quick double ended any debate around the result.
Story first published by: NRL.com