Derby County were beaten 4-1 by Sunderland in the Sky Bet Championship on Friday night.
Goals from George Honeyman, Ashley Fletcher, Aiden McGeady and John O'Shea secured victory for the visitors.
Matej Vydra scored in the first-half to take his tally to 19 for the season.
Forsyth created the first chance of the game for the home side when he crossed towards Andreas Weimann, but the Austrian couldn’t direct his effort on target.
Paddy McNair found the target with a vicious angled drive after 10 minutes, and from the resulting corner, the Sunderland fans were sent into raptures.
Honeyman picked the ball up outside the area and fired towards goal, and the touch from Forsyth took the ball past Scott Carson to put the Black Cats in front.
Derby struggled to launch attacks throughout the first period and the visitors doubled their lead nine minutes before the break.
Fletcher cut out Richard Keogh’s square pass to go through and after dodging the recovery efforts of the Derby skipper, he fired into the corner.
Vydra re-established himself as the Sky Bet Championship’s top marksman after 42 minutes, as he struck a superb volley into the top corner after Weimann’s knock-down.
Fletcher had a golden chance to restore the two-goal lead in added time, but he skewed his volley wide of the target.
Fortunately for him, Sunderland wouldn’t have to wait long to get their third.
When Forsyth brought down Lynden Gooch just after the break, the referee pointed to the spot, with McGeady taking the chance from 12 yards.
Fletcher went even closer to his brace just after the hour mark, when he cut inside and the struck the post.
Chris Coleman’s side hit the woodwork for a second time with 20 minutes to go, when Paddy McNair’s looping header bounced off the crossbar.
The Rams went down the other end immediately with Vydra and Cameron Jerome combining neatly, but the Czech shot well over the bar from the centre of the penalty area.
Soon after, Sunderland had their fourth when John O'Shea tapped home on the line following a corner.
Derby County: Carson; Baird, Keogh, Davies, Forsyth; Thorne (Nugent, 58’), Johnson; Weimann, Vydra, Lawrence (Palmer, HT); Jerome (Ledley, 83').
Substitutes not used: Roos, Pearce, Wisdom, Thomas.
Sunderland: Camp; Love, Kone, O’Shea, Oviedo (Matthews, 81'); McNair (Wilson, 77'), Cattermole, Honeyman; Gooch (Maja, 90'), Fletcher, McGeady.
Substitutes not used: Steele, LuaLua, McManaman, Robson.
Sunderland started well, but their opening goal came through a moment of good fortune.
Honeyman had space at the edge of the penalty area but his effort looked routine for Carson before the Derby No.1 was wrongfooted by a deflection.
One of the biggest positives of Derby’s season is that they have been able to call upon one of the league’s deadliest finishers.
Vydra’s efforts were in vain here, but the quality of his strike in the first-half shouldn’t go unnoticed, as he fired into the top corner to give Lee Camp absolutely no chance.
The Rams’ Easter weekend schedule concludes on Monday with the trip to face Preston North End at Deepdale, kick-off: 12:45pm.
Following that, Derby are back at Pride Park next Saturday, when Bolton Wanderers are the visitors.