Ulster racked up a bonus-point win over Edinburgh, 45-20, with six tries to take their season's impressive unbeaten run to nine games in all competitions and stay top of the RaboDirect PRO12 League.
However, the sight of Stephen Ferris hobbling off in the second half of his first game back in a month will raise further concern over his season.
Ulster made the worst possible start and it was little surprise that the visitors took the lead when winger Tom Brown crossed in the left corner after only 10 minutes, following Paul Marshall's fumble on Ulster's put-in.
Gregor Hunter's conversion was good and though Niall O'Connor -- on as a blood replacement for Pienaar -- slotted a penalty shortly after, Hunter's 19th-minute penalty saw Edinburgh deservedly lead 10-3.
Ulster responded after Roger Wilson stole an Edinburgh lineout. The home side swept up the field and after Chris Cochrane was denied in the left corner from a Jared Payne chip through, Ulster were awarded a penalty try.
Pienaar converted to level the scores and then helped launch an Ulster counter from the restart which saw Craig Gilroy steal down the left before putting Payne in for a 30th-minute try.
Four minutes later Hunter's kick was charged down by Pienaar who easily collected and ran in from 40 metres before converting to give Ulster a 24-10 lead and their third try in six minutes.
The Scots hit back when Brown barged over for his second three minutes before the break and Hunter's conversion made it 24-17 at half-time.
Hunter then made it 24-18 two minutes in before Ferris -- playing his first game in a month -- hobbled off the field, though the sight of a fully charged Nick Williams arriving clearly lifted Ulster's spirits.
He put himself about and with Ulster applying the screw, Marshall took a tap penalty under Edinburgh's posts and the ball was spun right to Wilson, who scored the bonus try in the corner.
Pienaar converted brilliantly and Ulster now led 31-20 before, after 68 minutes, Payne dashed over for his second under the posts which Pienaar again converted.
After the obligatory raft of substitutions, Gilroy finished the scoring with a try in the 80th minute which Pienaar again slotted home.