Match ends, Brighton and Hove Albion 2, Derby County 0.
Derby County dropped to second in the Championship as Brighton recorded a third consecutive win at home.
The Rams, wearing black arm bands in memory of club legend Dave Mackay, who died on Monday aged 80, created plenty of chances, but were punished for poor second-half defending.
Dale Stephens swept in a loose ball to put Brighton ahead and Kazenga LuaLua hammered in a second.
The result eases the Seagulls' survival fears, lifting them up to 18th.
A minute's applause was held before the game in honour of Mackay, who won promotion to the top flight as a player with Derby in 1969 and returned to manage them to the First Division title in 1975.
Those were golden years for the Rams, and while this current crop of players have put themselves in a strong position to restore Premier League football at Pride Park, their prospects have suffered a blow following back-to-back defeats, and they could drop out of the top two if Norwich beat Wigan on Wednesday.
Last week's loss at Fulham was a first in eight for Steve McClaren's side, but they were inches away from leading early on when Hendrick curled against the woodwork from 20 yards.
Richard Keogh also came close before the break, with David Stockdale tipping his header over the bar.
But Brighton, who have improved during Chris Hughton's two months in charge, went ahead when substitute Stephens reacted first to his own header and steered home from inside the box.
It had come after relentless Derby pressure, with Jamie Ward and Hendrick missing the best of a series of chances.
But the Seagulls stunned the visitors again, and put themselves nine points above the drop zone, when Chris O'Grady slipped in LuaLua, who had acres of space to finish.
Brighton manager Chris Hughton: "We showed great character against a very good footballing team. You can see why they are in this position.
"Had Derby scored in the first 15 minutes of the second half it would have been very tough for us.
"It's a very uncomfortable and nervy feeling to be only a point above the relegation zone, so certainly the feeling is more comfortable at this moment.
"Games come thick and fast and we must try and win some games away from home now."
Derby County manager Steve McClaren: "We dominated the game and played the Derby way; I thought we were excellent.
"Last Saturday we didn't deserve to win and tonight we didn't deserve to lose. I was pleased with what I saw; playing like that will give us results."
McClaren said he could dip into the loan market to cover for injured strikers Chris Martin and Darren Bent: "We are looking, but there is no problem to go again with Johnny Russell - he did a great job.
"He showed energy and a willingness to run, he is a centre-forward and he will score goals."
- 3GreerBooked at 45mins
- 30BennettBooked at 61mins
- 28KayalSubstituted forLedesmaat 90+5'minutes
- 17Vilaca TeixeiraSubstituted forStephensat 67'minutes
- 9BaldockSubstituted forLua Luaat 40'minutes
- 25Lua Lua
- 32ShottonBooked at 81mins
- 3ForsythBooked at 80mins
- 33MascarellBooked at 62minsSubstituted forDawkinsat 76'minutes
- 4BrysonBooked at 31mins
- 11RussellSubstituted forThomasat 76'minutes
- 10WardSubstituted forLingardat 72'minutes
- Neil Swarbrick
- Shots on Target
Second Half ends, Brighton and Hove Albion 2, Derby County 0.
Attempt saved. Chris O'Grady (Brighton and Hove Albion) left footed shot from the left side of the box is saved in the top left corner. Assisted by Kazenga Lua Lua.
Substitution, Brighton and Hove Albion. Emmanuel Ledesma replaces Beram Kayal.
Corner, Derby County. Conceded by Lewis Dunk.
Attempt blocked. Tom Ince (Derby County) left footed shot from the centre of the box is blocked. Assisted by Craig Forsyth with a cross.
Foul by Craig Forsyth (Derby County).
Bruno (Brighton and Hove Albion) wins a free kick in the defensive half.
Offside, Brighton and Hove Albion. David Stockdale tries a through ball, but Chris O'Grady is caught offside.
Foul by Richard Keogh (Derby County).
David Stockdale (Brighton and Hove Albion) wins a free kick in the defensive half.
Corner, Derby County. Conceded by Dale Stephens.
Tom Ince (Derby County) wins a free kick in the attacking half.
Foul by Beram Kayal (Brighton and Hove Albion).
Attempt blocked. Simon Dawkins (Derby County) right footed shot from the centre of the box is blocked.
Attempt blocked. Simon Dawkins (Derby County) right footed shot from the right side of the box is blocked.
Attempt blocked. Tom Ince (Derby County) left footed shot from the centre of the box is blocked. Assisted by Jeff Hendrick.
Ryan Shotton (Derby County) is shown the yellow card for a bad foul.
Foul by Ryan Shotton (Derby County).
Kazenga Lua Lua (Brighton and Hove Albion) wins a free kick on the left wing.