The first half started in explosive fashion as Johnson and Riihilahti missed excellent chances in the opening stages before Fulham lost Ian Pearce after six minutes for a professional foul on Johnson.
Johnson's early chance was a sign that the Cottagers had to be on their guard. The Palace hitman picked up a Joonas Kolkka pass on the left and cut across the area before letting fly from 15 yards out but Edwin Van der Sar reacted quickly to make a superb diving stop.
Palace's flying Finn Riihilahti was then left unmarked for a close-range header from Kolkka's cross, but the effort bounced a whisker wide of the post.
Fulham were clearly shaken and Zat Knight lacked the necessary composure when attempting to head to his central defensive partner Pearce. It left the ex-West Ham man struggling and he clumsily pulled down Johnson as the Palace striker advanced towards the Fulham goal.
Referee Mike Riley showed a red card for the professional foul and Fulham were down to ten with still another 84 minutes to go.
Strangely, it may have worked in Fulham's favour as Palace were given space and time to mount their attacks. But the early tempo dropped as Fulham sat back and Palace's attacks became more predictable as the half progressed.
Still Wayne Routledge shot wide after Adam Green hesitated to clear and Johnson also pulled a chance wide of goal.
However, Iain Dowie's outfit had a massive let off when Luis Boa Morte was put through by Steed Malbranque, leaving keeper Gabor Kiraly and Fitz Hall to make a combined tackle.
Boa Morte went down and all eyes turned to the referee's assistant as Riley was located on the wrong side, but the flag stayed down and home fans breathed a sigh of relief.
Palace started the second half with all guns blazing and got the inevitable breakthrough after 53 minutes.
Emmerson Boyce made ground from right to left before Riihilahti took over with a superb pass to the feet of Johnson.
The Palace striker took the ball in his stride before driving low past keeper Van der Sar, who got a faint touch before the ball nestled neatly into the far corner.
Eleven minutes later, the Eagles increased their lead. Routledge won a corner on the right and the Palace youngster took the kick himself. His out-swinger was met perfectly by Riihilahti who crashed a header into the roof of the net.
Fulham were just not in it and were lucky to survive a sure penalty claim when Johnson latched onto Kolkka's pass only to go down from Boa Morte's lunge. It looked a clear penalty as Boa Morte seemed to make no contact with the ball, but referee Riley, this time perfectly placed, judged no penalty.
Johnson then missed an absolute sitter after being put clean through. With only Van der Sar to beat he drove wide off the post from 12 yards out.
The Eagles continued to be wasteful as substitute Ivan Kaviedes hit the post from ten yards out after cleverly slipping past two defenders.
And near the end, Kolkka was in a great position to wrap up a good evening's work but delayed his shot a shade and the ball was deflected over the bar.
Fulham just couldn't wait for the nightmare to end while for Palace the only way is up.