He not only kicked five penalties and a conversion but charged down Toby Flood's clearance in the 58th minute to cross the whitewash for a crucial try to level the scores at 19-19.
Pienaar missed the start of the RaboDirect PRO12 season due to international commitments with the Springboks but has been a crucial player in recent weeks.
And Muller revealed the form of his teammate, who signed a new three-year deal with the club back in October, comes as no surprise to him.
"It seems like it's happening every week, when he scores all the points. I came here with him on Friday to do kicking practice and he did not miss one all day. He was outstanding and kicked them from 60, 62 metres," Muller told Sky Sports.
"From a captain's point of view it gives you a lot of confidence.
"A huge amount of credit to him and it doesn't just happen. He puts a huge amount of work in, he puts hours and hours into his kicking and it's wonderful when it pays off."
Victory over Leicester Tigers ensured Ulster finished as top seed in Pool 5 heading into the knockout stages, where they will face Saracens at Ravenhill in April.
It also gives the Ulstermen a chance to gain revenge for their quarter-final defeat to the same opponents in last year's competition, but Muller was not getting carried away.
"Sarries totally outplayed us last season," he added. "They are a great side and don't mind going away to get a result.
"It's two months away and at this stage we will just enjoy the moment. We have not achieved anything yet and there's a huge amount of work left if we are to achieve something."
"I have always said that in Europe we are representing not just the region but Wales as well."
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