They were joined by Sweden's Gabriel Hjertstedt as the only Europeans to break par in the pounds 1.65m event. The Ulsterman Darren Clarke struggled to a 74, alongside Germany's Bernhard Langer, the defending champion Ernie Els of South Africa and the Americans Mark O'Meara and Tiger Woods.
Seve Ballesteros fared even worse with a four-over-par 76 while Denmark's Ryder Cup man Thomas Bjorn will probably want to forget his 79.
Herron leads by one stroke from his fellow American Steve Lowery, with Dicky Pride another shot back on four under.
Fiji's Vijay Singh, the winner of last week's Honda Classic, and two- time Bay Hill runner-up Davis Love lead a group of 11 golfers on a three- under 69.
Laura Davies set her sights on a fifth Standard Register Ping title, she has won the event a record four times in succession since 1994, with a first round four-under-par 68 at Moon Valley in Phoenix, Arizona.
While Canada's Dawn Coe-Jones birdied the 18th to lead on seven under, Davies highlighted her round with an eagle three at the 490 yards eighth hole - where she hit a four-iron second shot 220 yards to 15 feet.
Meanwhile, Pat Bradley, a six time major winner, was named as the American captain for the 2000 Solheim Cup at Loch Lomond. A three-time Solheim Cup player, including the only US defeat, at Dalmahoy in 1992, she takes over from Judy Rankin, who has stepped down after two terms.
The Cup format is also to be changed with eight foursomes on Friday, six fourballs on the Saturday and 12 singles on the Sunday. Previously, it was the same as the Ryder Cup, with four foursomes and four fourballs on the opening two days.
"Pat will be a great captain - she deserves the honour," said Davies, who also agreed with the change in format. "It is to fit in with the daylight hours and I think it is a good idea."Reuse content