Brighton suffered their first league defeat since August at Hartlepool.
Pools opened the scoring, defender Neil Austin meeting Antony Sweeney's headed pass and nodding in from close range.
The Seagulls drew level when Kazenga LuaLua crossed low for Gary Dicker to fire home, before Pools went ahead through Gary Liddle's close range shot.
Brighton midfielder Liam Bridcutt saw red for a lunge on Liddle, before Hartlepool made it three with James Poole's thumping header.
Brighton boss Gus Poyet told BBC Sussex: "I'm pleased that we are making the opposition think about us. They changed their style to play us.
"We had a great chance to score but didn't, then they got the goal out of a mistake. When you're in control you need to finish.
"It was a great challenge for us to come back. We went a little bit more offensive and it looked like we were going to win the game until the sending off. When we went to 1-1 I though the game was ours."
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