Bridgend fought back from 13-20 at halftime as Havili's pace proved too much for the Drovers, but the Tongan international gave the home fans a few nervous minutes when his high tackle gave Llandovery a 78th-minute penalty try.
At Aberavon's World of Hurt ground, Llanelli's Mark Jones gave Wales coach Steve Hansen a late Christmas present with a stunning return from injury, but his second-minute try was in vain.
The World Cup winger picked up a loose ball on his own try-line and left the Aberavon defence for dead in a 90-metre sprint to open the scoring, but Aberavon fly-half Jamie Davies brought up 200 points for the season by scoring 20 in his side's 25-20 victory.
In further bad news for the visitors, scrum-half Adrian Williams left the field on a stretcher midway through the second half.
Veterans Dale McIntosh and Neil Boobyer both scored tries as Pontypridd came from behind to beat Newbridge 21-9.
Results: Aberavon 25 Llanelli 20, Bridgend 35 Llandovery 34, Newbridge 9 Pontypridd 21.