Second-rower Angus Crichton scored his second career hat-trick as the Roosters went to 36 points on the ladder with their win at Robina and ousted Penrith from second based on a superior for-and-against.
The Tricolours can wrap up a top two finish if they beat Canberra and South Sydney in their remaining matches.
The Roosters lost Waerea-Hargreaves to the sin-bin in the 12th minute when the firebrand was put on report for an incident in the lead-up to a try to Titans winger Alofiana Khan-Pereira.
Waerea-Hargreaves, in his first game back from a four-match suspension, was pinged on review by The Bunker for forceful contact to the head of Titans hooker Sam Verrills .
Due to his prior offences, a grade two charge by the match review committee would lead to a three-match ban.
If the Roosters don't make the top four and were to lose their opening final, unlikely though that is, that would be the end of Waerea-Hargreaves' NRL career. The three-time premiership winner will join England's Hull Kingston Rovers next season.
The Roosters lost centre Joseph-Aukuso Suaalii to a shoulder injury in the first half but early reports suggested it was less serious than first feared.
Roosters hooker Brandon Smith was a late withdrawal with injury and was replaced by Zach Dockar-Clay, who charged through the middle early before forward Angus Crichton scored the opening try in the fourth minute.
The Titans hit back with Khan-Pereira scoring the first of his three tries of the afternoon.
Roosters No.6 Luke Keary put a deft lob in for winger Dominic Young to score in a sublime piece of skill by the veteran.
Khan-Pereira then beat opposite number Dom Young twice, Joey Manu and James Tedesco in a 90m run to the line in which he didn't run at full pace once in a remarkable display of athleticism.
Roosters half Sam Walker went over and winger Daniel Tupou scored a double in a try blitz before halftime for the visitors to take a 26-10 lead.
When skipper Tedesco scored the first try after the break the result was sealed. The Roosters then ran riot as only they can.
Titans second-rower David Fifita and his counterpart Crichton played out an engrossing battle within the battle - understandable considering Fifita backflipped on joining the Tricolours earlier in the season.
