Giant back-rower Dave Taylor gave the visitors the lead after putting a big left-foot step on fullback Will Hopoate before powering over the line.
The Eels struggled with their cohesion, much to the frustration of the home crowd but - after forcing the Titans to defend back-to-back sets - finally managed to get on the scoresheet through Danny Wicks.
It was the prop's first NRL try since round 10 in 2009 on a day the former Newcastle forward signed a new one-year contract.
But from the resulting kick-off, Anthony Watmough threw a poor pass and Roberts reacted quickest to nip in front of John Folau and score under the posts.
Reece Robinson then crossed for the hosts a minute later with Chris Sandow converting from the sideline to level the scores at 12-12.
Hopoate barged over just before halftime to give the home side the lead at the break, but it was all one-way traffic in the second half, as the Titans powered to their second win of the season as the Eels were held scoreless after halftime for the second week in succession.
After turning over the ball four times after halftime, the home side managed to hold out Neil Henry's side.
But they were made to pay when a poor offload from Corey Norman fell short of Folau and, from the resulting scrum, Roberts linked up with Aidan Sezer to score his second.
The 23-year-old added his third to effectively seal the victory when he picked off Nathan Peats' lazy pass and sprinted 70 metres to touch down under the posts.
That setback knocked the fight out of the Eels and the Titans added two more tries through William Zillman and David Mead before Anthony Don added some extra gloss to the emphatic scoreline with a late four-pointer.
- AAP
