Rose, who was 1 over at the turn, had four birdies over his last nine holes. The Englishman was at 4-under 138 after two rounds and was only player in the 55-man field under par.
"I'm very focused right now and I'm staying in the moment and that's why I'm playing so well," Rose said. "We're nowhere near the finish line, so it's still very much just going about my business, and the same old boring stuff, one shot at a time."
Harrington, who won the Order of Merit money title here last year, had birdies at the fourth and fifth holes before a bogey at the last gave him a 71 for the day and even-par for the tournament.
"It's very much game on for the tournament and game on for the Order of Merit," the Irishman said.
Harrington leads Rose by $948 in the European Tour standings. With the winner of the Volvo Masters earning $960,488, both are in position to overtake Order of Merit leader Ernie Els, who holds a $313,892 advantage over Harrington but opted to play in Singapore on the Asia Tour this week.
Rose nearly had a hole-in-one at the par-3 third for the second straight day, sticking it close to the pin before making birdie.
But after missing a 5-footer for birdie at the fourth and getting bogeys at the fifth, seventh and ninth, Rose decided to play it safe.
"This golf course really lends itself to boring play; (hitting) the middle of the green is never a bad thing," he said.
Harrington, the British Open champion, had 11 straight pars in a much more consistent round after Thursday's up-and-down day.
"Strategy-wise, you have to go along like it's a Major," he said.
First-day leader Graeme McDowell (75) of Northern Ireland was joined by Spain's Miguel Angel Jimenez (70), Soren Kjeldsen (70) of Denmark and India's Jyoti Randhawa (70) in a tie for third at 1 over.
With the soft course playing so tough with strong winds that aren't likely to let up, organizers said the rough inside the ropes would be slightly lowered for the final two days.