Cardiff City booked their place in the Championship play-offs after coming from behind at Crystal Palace.
Palace striker Wilfried Zaha gave the hosts a first half lead when he tucked home Darren Ambrose's defence-splitting through ball.
But Peter Whittingham curled in a free-kick to draw Cardiff level shortly after the restart.
And Don Cowie ensured his side would finish sixth in the table when he lashed in Mark Hudson's flick-on.
Mackay delight at play-off place
Cardiff knew a win at Selhurst Park would guarantee a play-off place but were also aware that defeat, coupled with a Middlesbrough victory at Watford, would see the Bluebirds slip out of the top six.
The visitors started brightly and almost took the lead three minutes in when Lewis Price, playing in goal in place of the injured Julian Speroni, denied Joe Mason at close range after initially spilling Liam Lawrence's 20-yard shot.
Semi-finals first leg
Cardiff v West Ham (1945 BST)
Blackpool v Birmingham (1945)
Semi-finals second leg
West Ham v Cardiff (1630)
Birmingham v Blackpool (1945)
The save seemed to jolt Palace into life and they soon took the lead when Zaha played the ball to Ambrose before racing onto the midfielder's fine through pass to finish under the advancing David Marshall from the edge of the Cardiff penalty area.
Cardiff supporters remained in fine voice at the interval, despite their obvious nerves, and they were soon celebrating when top-scorer Peter Whittingham curled home a free-kick from the narrowest of angles eight minutes into the second half for his 13th of the season.
The goal galvanised Cardiff's play and they took the lead when captain Mark Hudson flicked-on Aron Gunnarsson's long throw and Don Cowie turned in the box to fire home into the bottom corner of the Palace net.
News soon filtered down from the terraces that Watford were
winning 2-1 against Middlesbrough
and as the final whistle blew and Cardiff's play-off place was confirmed, Cowie and Whittingham led the celebrations with the jubilant Bluebirds supporters.
Crystal Palace manager Dougie Freedman:
"I had a plan at the beginning of the season and the plan was to take the club up to the next level in terms of not fighting relegation battles.
"We did that 10 games ago and that gave me the opportunity to blood one or two young players and get more experience for them.
"In the middle of that we went on a fantastic cup run which gave a lot of exposure to the club for the right reasons."
Cardiff City manager Malky Mackay:
"We are 10 games unbeaten going into the play-offs so there is real momentum there.
"I have been in the semi-final situation as a player with West Ham, Norwich and Watford. It is about staying calm and having a game plan."
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