Rose, who started the round with a four-shot lead atop the leaderboard, recovered from a bogey-double bogey start with three birdies and then sank a tough putt at the last hole to save par.
'A four-shot lead is nothing to be excited about, as I proved after two holes,' said Rose, who is at 4-under 209.
Harrington had drawn even with Rose by the third hole after a birdie at the first, but needed another birdie at the 17th to shoot a 71. The Irishman is tied with Simon Dyson (69) of England at 213.
'It's in his hands tomorrow,' Harrington said. 'It would be silly not to think there isn't pressure on us both. We'll wait and see tomorrow night who handled it the best.'
Ernie Els leads the European money title by $313,892 over Harrington, but opted to play in Singapore on the Asia Tour this week.
Harrington, who won last year's Order of Merit money title at this event, leads Rose by $948.
Rose needed three putts at the first hole after his pitch rolled backward to leave him 60 feet short of the pin.
The Englishman overshot the green with his approach at the second, and then flubbed two wedge shots before his 9-foot putt slid past for a double bogey to be tied with Harrington at 1 under.
'I was obviously shell-shocked -- it wasn't the start I was looking for,' Rose said. 'On the third tee, I just said to myself: 'You're still joint leader of the tournament, let's take it from there.''
Despite a tricky pin position at the third hole, Harrington didn't lay up as he did in the opening two rounds and his ball bounced sharply off a rock to leave him with a tough chip over water.
The Irishman didn't make it and needed to sink a 5-footer for a bogey, but Rose had retaken the lead.
'I played three good holes and was feeling very good about my game and feeling very confident,' Harrington said. 'If (the shot) came off, you're expecting to make birdie.'
Rose's driving was inconsistent on the front nine, but he improved on the back to roll in birdies at the ninth and 11th. Although he needed to get up and down from a bunker at the last hole to save par.
'I putted a lot better today and that was the key,' Rose said. 'I'm just trying to win this tournament, it's as clear as that. The goal is a simple equation, which is: if you win, you win (the Order of Merit).'
Dyson, one of only six players in the 54-man field to finish under par, will partner Rose for the final round, while Harrington plays with 2004 winner Ian Poulter (69).