Harlequins lost their first Super League game under their new identity as St Helens romped to a 40-16 victory.
Harlequins (6) 16
Tries: Smith, Sheriffe, Sykes
Goals: Gafa, Sykes
St Helens (24) 4o
Tries: Cayless, Wellens 3, Gardner, Hooper, Lyon
Goals: Lyon (6)
Great Britain full-back Paul Wellens ran in a hat-trick of tries as Harlequins were left reeling after a first-half points blitz.
Wellens crossed twice with Ade Gardner also going over after Tyrone Smith had cancelled out Jason Cayless's opener.
Rikki Sheriffe replied but Wellens got his third before Jason Hooper and Jamie Lyon put the match beyond Harlequins.
Paul Sykes' consolation try came too late for the home side to attempt to reel in Saints further.
Quins started the game with a new name, a new home at the Twickenham Stoop and a new kit but Saints quickly took the shine off their fresh start.
The home side tried to force the pace but handling errors were their undoing and the visitors demonstrated the gulf in class that could not be disguised by their revamped appearance.
Harlequins head coach Tony Rea:
"It's a positive day for the club and a miserable day for the team.
"It's disappointing because it was a great day for rugby league in London. Maybe the occasion meant we were thinking too much about other stuff.
"We have to hope that people will give us a second chance and we'll put on a different performance for them."
St Helens coach Daniel Anderson:
"It's hard this time of year because you think you've prepared well but both teams were scratchy.
"We'll both be much better for it - our skills will sharpen up. There was a lot of dropped ball because it was the first game of the year.
"I don't think most teams will be ready until round four or five."
Harlequins: Gafa, Sheriffe, Lucky Luisi, Smith, Bradley-Qalilawa, Dorn, Leuluai, Temata, Weisner, Heckenberg, Purdham, Hopkins, Williams.
Replacements: Haumono, Mills, Sykes, Tookey.
St Helens: Wellens, Gardner, Lyon, Talau, Meli, Pryce, Long, Fozzard, Cunningham, Cayless, Gilmour, Wilkin, Hooper.
Replacements: Roby, Graham, P. Anderson, Fa'asavalu.
Referee: R Silverwood (Dewsbury)