The giant Tongan tighthead now has 11 tries in all competitions and four in his last four Aviva Premiership games. His two scores, in addition to tries from Guy Armitage (two), Sailosi Tagicakibau, Chris Hala'ufia and Matt Garvey saw Irish run riot.
For Welsh, who are already guaranteed to finish bottom of the table, it was a case of what might have been as the boot of Gordon Ross and tries from the impressive Seb Stegmann and Nick Scott kept them close for a while.
Former Scotland fly-half Ross was off target with a couple of early penalties but was unerring thereafter from the kicking tee, opening the scoring with his third attempt in the sixth minute. Irish's first try came from Armitage just moments later, the centre breaking a couple of tackles after being fed by Tom Homer. Ian Humphreys added the conversion.
Stegmann, who was playing at outside centre rather than on the wing, had already made two clean breaks in the opening exchanges but both times Lyn Jones' side failed to make the most of the initial advance. Former Quins man Steggman went over for Welsh's first try, diving over to make it 8-7 to the visitors. Ross failed with his conversion attempt.
And it was Welsh who were first to score their second try - somewhat against the run of play - on the half-hour mark. Stegmann was again involved with a fine initial break that saw Scott dive over in the corner, Ross' conversion taking it to 15-7.
But Irish were soon back in contention and it was that man Aulika, the prop diving over from close range with Humphreys' conversion making it 15-14 to the visitors. And Irish were back in front before the break. Marland Yarde was tackled centimetres short of the tryline and Hala'ufai found space to barrel over to make it 19-15.
Straight after the interval Aulika bagged his second, picking up and driving over from close range as Hala'ufia forced his team-mate over the line. Humphreys' conversion went over off the post to put Irish 26-15 to the good, but Welsh were not going to roll over and Ross' two penalties in quick succession meant Welsh only trailed by five points.
Still it was Irish who carried the greater attacking threat, though, and only a George Skivington knock-on prevented their fifth try of the game. With Aulika desperately searching for his hat-trick it was Tagicakibau who scored the decisive try on 61 minutes. He went over in the corner, with Humphreys' conversion stretching the lead to 33-21.
The departing Garvey then celebrated his last game in Irish colours with the sixth try before Armitage powered over for his second, with Greg Bateman adding a late consolation score for the visitors.