Westwood and Kang dropped back into joint second place, a stroke behind Chang after both players added a 69 to their 66 on the opening day.
"I didn't feel on top form," said Westwood, who finished tied sixth in last week's US Masters. "Physically I didn't feel great. I woke up very early with the jet lag. I can't do anything about that. I am getting a bit tired after five weeks on the trot. The flight across has caught up with me. I definitely feel a bit sickly tired today."
The Englishman managed to birdie three out of his last six holes to stay in contention. "I wasn't feeling particularly well before I went out so I wasn't looking for a great deal. I woke up at 5.30 this morning," said Westwood.
Chang, a distant cousin of the tennis player Michael Chang, had no such problems and made an eagle, six birdies and two bogies over the 6,662- yard par-71 course. His round was completed in sensational fashion when he holed a 50-foot putt for a birdie.
Chris Williams, who opened with a 67, slipped back with a second-round 72 to be five shots off the pace while Darren Clarke added a 70 to his opening 72 to lie eight strokes behind Chang.
Nick Faldo has made an encouraging start to the MCI Classic at Hilton Head in South Carolina as he attempts to resurrect his season and earn a place in Europe's Ryder Cup team. Cup captain Mark James has warned Faldo he can expect no special treatment as he struggles to qualify for the European team to face America in September.
The former world No 1 has slumped to joint 99th in the rankings following an appalling run of form and is currently only 39th in the Ryder Cup points table. The six-times major winner's woes continued at the Masters last week when he shot 80 in the first round and missed the cut for the third straight year since winning his last major at Augusta in 1996.
However, the 41-year-old fired a two-under-par first-round 69 at the windswept Harbour Town Golf Links to finish in a group of 14 players four shots behind the joint leaders, Jeff Maggert and Steve Flesch.
Colin Montgomerie is two shots further back on the level-par score of 71.
Sergio Garcia, who with Jose Maria Olazabal celebrated a brilliant Spanish double at the Masters last Sunday, has confirmed that he is to make his professional debut at the Spanish Open next week. Hours before Olazabal won his second Masters title the 19-year-old Garcia clinched the silver cup awarded each year to the leading amateur at Augusta.Reuse content