The All Black winger claimed a brace to move above compatriot Christian Cullen and drew level with the former Brumbies and Australia on 57 career tries.
The tournament leaders went 15-0 ahead of the fourth-placed Traansvaal side within 10 minutes and had the bonus point wrapped up within half an hour.
Within four minutes, number eight Nick Williams opened an opportunity for scrum-half David Gibson to set up a move finished by veteran fly-half David Holwell.
And two minutes on, Rudi Wulf went in with a similar move also ending up with a try on the left wing.
Holwell's eighth-minute penalty extended the advantage, but the Lions came back into the game.
Having gained some territory, Blues full-back Ben Atiga fumbled Andre Pretorius' high kick, allowing Louis Ludik to capitalise.
But the Blues hit back with interest. After the Lions were given the benefit of the doubt after Williams crossed the try line, the prolific Howlett left no room for conjecture with a short-range dash, with Atiga then making amends for his earlier error.
Flanker Daniel Braid tunnelled over to give his team a 34-7 interval lead.
The second half was a scrappier affair, but Howlett's record-equalling try was converted by Holwell.
Hooker Etienne Reynecke scored a last-minute consolation, but the Blues had already reaffirmed their championship aspirations.