Taylor, now back at middleweight where he once reigned supreme, beat the over-matched but brave Jessie Nicklow inside eight rounds, while Dirrell stopped Darryl Cunningham in two.
The pair had been sidelined for 26 and 21 months respectively - Taylor in particular taking time to asses his future prospects after losing four of his last five fights.
Knockouts by Carl Froch and Arthur Abraham had left question marks over "Bad Intentions'' career prospects, but the 33-year-old is now looking to challenge for one of the middleweight titles after dropping back to the 160lb limit.
Taylor, who admitted afterwards to being rusty on his return, was deducted a point for hitting after the bell to end the sixth but had won virtually every round before the referee stepped in to spare Wicklow further punishment.
Dirrell floored Cunningham twice in the second round on the same card in California, first from a long left hand and then a short right.
Also on the same card, the former Cuban amateur Luis Garcia made an impressive American debut with a lop-sided points verdict over Alexander Johnson.
Light-heavyweight Garcia, now based in Cork, moved to 12-0 with nine wins by stoppage. Stablemate Mike Perez, who won last year's International Prizefighter, dominated a 10-rounder against durable Nigeria-born Friday Ahunanya.