The changes at the top continued almost minute by minute.
Former World Number One Martin Kaymer was first to nine under with an eagle on the first, but was then joined when McIlroy and Willett birdied the same hole and Paraguay's Fabrizio Zanotti started with two in a row.
After Boyd and Donaldson began with birdies there had already been 12 different players in at least a share of the lead on the day.
Ireland's Peter Lawrie and Scot Stephen Gallacher got in on the act, becoming part of a nine-way tie on nine under.
Recent Irish Open winner Dyson, though, made a poor start, failing to birdie the long first and then bogeying the par three third to slip two behind and all the way to 16th along with, among others, Lee Westwood.
|T3||VAN ZYL, Jaco||RSA||18||-15|
|T6||ANDERSSON HED, Fredrik||SWE||18||-14|