The pair each claimed first goals for the club at the Stadium of Light as the Black Cats saw their hopes of a cup run go up in smoke.
Grant, who made seven changes to the side which drew at Stoke at the weekend, was rewarded with a performance which thoroughly warranted a first victory of the season over top-flight opposition.
He said of Piquionne and Obinna: "They worked very hard, they moved very well and they played well together - but all the team behind them played well.
"We passed the ball very well in the midfield so it was more easy for them to find space to score two fantastic goals.
"We want to play always with the same style, this is our target. If you saw our last games, except the first one against Aston Villa, we have been playing the same all the time.
"Always we progress and progress and today, it was the same game as against Chelsea, but with a result."