Campbell showed his Major credentials by signing for a 64 to take the second round lead on nine-under-par 131 while Spain's Miguel Angel Jimenez and Sweden's Fredrik Andersson Hed are tied for second with Zhang on 132.
Denmark's Anders Hansen, who had taken the morning round lead earlier, was in fifth place after rounds of 69 and 64 while Asian Tour members Javi Colomo of Spain and Japan's Daisuke Kataoka shared sixth place on 135 at the Hong Kong Golf Club.
Having gone without a win since lifting the US Open title in 2005, Campbell continued his golf revival by moving atop the leaderboard for a well-deserved lead.
Campbell has climbed from 910th place on the official world golf ranking four months ago to 339th, thanks largely to his third place finish in Portugal last month.
"Today was a day where I played great from tee to green and holed a few nice putts for pars and birdies. But I'm just happy to be in a position to have a chance for the weekend. That's why we play the game. That's why I didn't give up. That's why I just stuck at working hard on my game, and I knew that this would happen. I deserve it, really," said Campbell.
Zhang continued to delight the local galleries with another impressive performance as he bids for a unique treble having won the National Opens of China and Macau on the Asian Tour.
"As a Chinese, winning the UBS HK Open will be a significant milestone for my career as that would mean capturing the three National Opens of each country. I want that," said Zhang.
Remarkably, the 47-year-old veteran could have even snatched a share of the lead with Campbell at the last had his birdie putt not stopped inches away from the hole.
"It was a heart-stopping moment for me too," laughed Zhang. "But overall, I'm happy with the way I played. I've been very consistent and the results are showing. I've known Campbell for a long time and I look forward to playing together with him."
With three top-10 finishes this season, Colomo is hoping that he can end his rookie year on the Asian Tour with a flourish.
"I played very solid from the tee again but unfortunately I didn't have much luck on the greens. The strong winds also made it very difficult today. But I'm happy with how I fought all the day starting from the first hole," said Colomo.
Colomo is delighted that he has managed to upstage the marquee names and is confident that he can carry his solid run of form into the weekend rounds.
"I enjoy the pressure of playing with all these star players this week. For me, it gives me lots of satisfaction knowing that I can beat the world number one and many of the other great players," said Colomo, who earned his Tour card by finishing tied-ninth in Qualifying School in January.
World number one Rory McIlroy of Northern Ireland will not be defending his title as he made his early exit after rounds of 73 and 72.
"Hong Kong's a great place and this is such a great tournament. I always enjoy coming back. Just a pity that this year it had to end like that," said McIlroy.
Marcus Fraser leads the Australians in a share of 8th position five shots behind the leader.
The cut was set at two-over with a total of 73 players making the cut.
Leading scores after round 2 of the UBS Hong Kong Open Championship 2012 being played at the par 70, 6699 Yards Hong Kong Golf Club course (a- denotes amateur):
131 - Michael CAMPBELL (NZL) 67-64.
132 - ZHANG Lian-wei (CHN) 66-66, Miguel Angel JIMENEZ (ESP) 65-67, Fredrik ANDERSSON HED (SWE) 66-66.
133 - Anders HANSEN (DEN) 69-64.
135 - Javi COLOMO (ESP) 64-71, Daisuke KATAOKA (JPN) 68-67.
136 - Marcus FRASER (AUS) 67-69, Peter LAWRIE (IRL) 68-68, Ricardo SANTOS (POR) 71-65, Stephen GALLACHER (SCO) 68-68, Arnond VONGVANIJ (THA) 71-65.
137 - Matteo MANASSERO (ITA) 67-70, David HORSEY (ENG) 67-70, Mark FOSTER (ENG) 69-68, Jose Maria OLAZABAL (ESP) 66-71, James MORRISON (ENG) 70-67, Mardan MAMAT (SIN) 67-70, Kwanchai TANNIN (THA) 68-69.
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