Mitchell pounced on a grubber from second-rower Brad Takairangi, grounding the ball centimetres inside the deadball line for the night's most unlikely try.
Roosters centre Mitchell Aubusson also crossed in the first half, palming off opposition halfback Shaun Johnson on his way to the tryline as the home side dominated field position and possession, as well as the scoreboard.
A late try to Jerome Ropati for the Warriors reduced the lead to 12 before the halftime break.
But there simply wasn't enough in the tank for the Warriors in the second half as the Roosters' big men muscled up against their more-fancied opposing pack.
Only a 40-metre screamer from Warriors fill-in fullback Glen Fisiiahi gave the impression the Kiwis might mount a fightback, but errors continued to haunt them, as Braith Anasta kicked two penalty goals to keep the scoreboard ticking over.
Anasta was well and truly on his game despite signing a two-year deal with Wests Tigers during the week, leading the Roosters around the park in a composed display, while fellow veteran Anthony Minichiello, who scored in the final minute of the game, was outstanding at the back.
Roosters enforcer Jared Waerea-Hargreaves was among the best on the field but may find himself in trouble with the match review panel after he was put on report in the 55th minute for a high shot on Ukuma Ta'ai.
SYDNEY ROOSTERS 26 (M Aubusson S Kenny-Dowall A Minichiello A Mitchell tries B Anasta 5 goals) bt WARRIORS 8 (G Fisiiahi J Ropati tries)
- AAP
