Padraig Harrington and Prayad Marksaeng each carded 3-under 67s. Both men bogeyed the 18th hole though to slip into a share of second place at 7-under-par 203.
Hanell began the round at Hong Kong Golf Club seven strokes behind Richard McEvoy, the leader after each of the first two rounds. Hanell picked up his first birdie at the par-5 third.
The 30-year-old Swede ran home back-to-back birdies from the sixth to get to 6 under. Around the turn, he birdied the 10th to get to minus 7.
Hanell ran off six straight pars from there. He sank his fifth birdie of the round at the 17th to cap a bogey-free round and join the leaders at minus 8. Harrington, Marksaeng and McEvoy, who were all 8 under at the time, would all drop shots to give Hanell the overnight lead by himself.
'I am very happy,' said Hanell, who is searching for his first tour victory. 'There were no blemishes on the card and it feels great to be up on the leaderboard. I feel great right now.'
Harrington moved to 5 under with birdies on the third and eighth. However, he stumbled to a bogey at the ninth. On the back side, the Irishman atoned for that mistake with a birdie at No. 10.
The two-time winner last season then holed out for eagle from a greenside bunker at the par-5 12th to get to minus 8. He could not hold on down the stretch though.
Harrington bogeyed the 16th, but came back to birdie 17 to regain a share of the lead. However, he three-putted for bogey at the last to drop into a tie for second place.
Marksaeng, playing alongside Harrington, also began the day at minus 4. He fell farther off the pace as he bogeyed the first. Marksaeng rallied with consecutive birdies from the third to get to minus 5.
The Thailand native birdied Nos. 6 and 10 to get to 7 under. He grabbed a share of the lead with a birdie at the 13th. He also three-putted for bogey at the last to fall out of the lead.
McEvoy, the medalist at the 2003 European Tour Qualifying School Tournament, bogeyed each of his first two holes to drop back to 8 under. He halted the slide with a birdie at the third though.
The Englishman fell back to minus 8 as he dropped a stroke at the eighth. He lost his share of the lead when he bogeyed the 14th and dropped into a share of fourth place with a bogey at the last.
McEvoy is joined in fourth place at 6-under-par 204 by Chris Gane (67), Rob Rashell (67) and last year's winner Fredrik Jacobson (71).
Thomas Bjorn and Hennie Otto are one stroke further back at minus 5. Darren Clarke headlines a group at 4-under-par 206. He is joined there by Gary Rusnak, David Carter, Adam Fraser and Barry Lane.