Defending champion Barry Lane posted a 2-under-par 70. He was joined in a tie for fifth place by Stephen Dodd, Scott Drummond, Richard Finch, Pierre Fulke, Soren Hansen, Andrew McLardy and Angel Cabrera, who shared second place behind Lane last year.
Howell, a member of the victorious 2004 European Ryder Cup squad, got off to a quick start as he birdied the first. He came right back with a chip-in birdie on No. 2 on the Arden Course at the Marriott Forest of Arden Hotel & Country Club.
The 29-year-old Howell dropped in his third birdie putt on the par-4 fourth. The 1999 Dubai Desert Classic winner again made it two in a row as he birdied the fifth to move to 4 under. He reeled off 12 consecutive pars before stumbling to a bogey at the last when he was unable to get up and down to save par.
'That is a pretty good score today,' said Howell. 'I played the tough holes really well, gave myself some birdie chances, but let myself down a little on the par-5s by not hitting the fairways and laying up all the time.'
Davis opened with a birdie on the fourth. However, he faltered to bogeys at six and nine to make the turn at plus-1. The Englishman jumped to minus-1 thanks to an eagle on the par-5 12th.
The 29-year-old, who won the 2004 ANZ Championship, slipped to another bogey on the par-4 14th but Davis closed with a flurry. He drained a birdie try on the 16th and came right back with a birdie on 17.
Davis capped his round off in fine fashion as he chipped in for his third straight birdie on No. 18 to end at minus-3.
'It was a real struggle,' Davis said. 'I putted really well, but just couldn't hit it. But I managed to get my way around. It was just one of those days to hang in there.'
Mason got going with a birdie on the par-4 second. He moved to 2 under with a birdie on the fourth. After stumbling to a bogey on No. 6, Mason holed consecutive birdie tries from the seventh to make the turn at minus-3.
Around the turn, Mason climbed to 4 under with a birdie on the par-5 12th. Mason slipped back to 2 under with bogeys on the 14th and 17th. He managed to share the lead as he rolled in a 6-foot birdie putt on the closing hole.
Lynn was the lone leader to begin his round on the 10th tee. He struggled to a bogey on that hole, but got back to even par with a birdie on the 12th. The Englishman tripped to another bogey on the 13th.
The 31-year-old notched back-to-back birdies at 16 and 17 to get to minus-1. Lynn again birdied consecutive holes from the third to join the leaders at minus-3. He picked up another birdie on the seventh, but stumbled to a bogey at the next to come in at 3 under.
Simon Khan, Peter Baker, Robert-Jan Derksen, Simon Dyson, Stephen Gallacher, Marcel Siem and Patrik Sjoland were the final players in red figures at 1-under-par 71.
Colin Montgomerie, the 1998 champion here, looked like he would end as one of the leaders as he went to the ninth, his last, at minus-3. However, after a lengthy delay on the tee, the Scotsman struggled to a triple bogey to finish at even-par 72.