The midfielder scored the opening goal after just 39 seconds but later saw a spot-kick saved by Royals keeper Alex McCarthy.
However, boss Dougie Freedman said: "I know how Darren is feeling, he scored a fantastic goal and then missed a penalty.
"Make no mistake, Darren Ambrose will take the next penalty, and if he misses he'll take the one after that.
"He is one of the best strikers of the ball at the club. There is no blame at all, he is the kind of guy who next week will stand up, take the next penalty and score it."
Source: PA
Source: PA