The Hampshire all-rounder has signed a short-term deal with the franchise, who are captained and coached by the iconic bowler, Shane Warne.
Mascarenhas was involved in England's one-day side in the recent tour of New Zealand but has admitted his involvement in the IPL could hinder his international prospects.
The Royals used Warne, Graeme Smith, Shane Watson and Sohail Tanvir as their four internationals.
But the star performance came from Swapnil Asnodkar, the man from Goa thumping 60 from 34 balls.