Back-rower Jacob Host, playing his fourth NRL clash, charged on to a short pass from Widdop to score in the 10th minute and Widdop converted to extend the Dragons' lead to 10-0.
When centre Euan Aitken took a Marshall pass to stroll over and score the Dragons' third try for a 14-0 lead, Knights fans must have feared yet another blowout.
But the Newcastle faithful had cause for celebration when acrobatic winger Nathan Ross vaulted the corner post to touch down in the 30th minute.
Trent Hodkinson's sideline conversion cut the deficit to 14-6 but the comeback was short-lived.
Marshall's cut-out pass in the 35th minute set up a try for left centre Tim Lafai, then Marshall skipped away from Jacob Saifiti to scoot away and score in the final seconds of the half.
Tempers frayed in the 43rd minute when Dragons back-rower Joel Thompson resented a play-the-ball shove from new Knights winger Brendan Elliot and responded in kind. From the subsequent penalty, Thompson trampled over the top of Sione Matautia and Dane Gagai to score and Widdop converted to stretch the lead to 28-6.
The offload by Knights forward Robbie Rochow and Gagai's grubber kick set up a consolation try for Matautia in the 65th minute, which Hodkinson converted to trim the deficit to 28-12.
Former Raiders forward Mitch Barnett pushed through Tyson Frizell's attempted tackle on the goal-line to score Newcastle's third try in the 73rd minute and Hodkinson converted, adding further respectability to the scoreboard.
Ross conceded a professional foul in the 79th minute and finished the game in the sin-bin, gifting Widdop a penalty goal to end the scoring.
- AAP