Swede Mathias Gronberg, called in when Nick Faldo withdrew because of an illness in his family, shared the early first-round lead in the Honda Classic in Palm Beach Gardens, Florida.
The former European Tour winner, who celebrates his 36th birthday on Sunday, had five birdies in his first 12 holes to be alongside Japan’s Daisuke Maruyama - another graduate of last December’s US Tour qualifying school.
Gronberg followed birdies at the first, fifth and sixth by hitting his tee shot to five feet on the short eighth and then almost holed a bunker shot at the 588-yard 12th.
Compatriot Jesper Parnevik was in the group only two back – but after two birdies in his first three holes, defending champion Padraig Harrington double-bogeyed the 16th and did well not to do the same on the 18th.
The Dubliner drove in the water there and hit his third shot into a greenside trap but limited the damage to a bogey with a 10-foot putt.
Harrington, who fired a closing 63 last year and then won a play-off when Vijay Singh missed from under three feet, remained one over par with eight to play. Brian Davis and Ian Poulter were one further back – Poulter after dropping three shots in his first two holes.
Lee Westwood and Greg Owen were among the later starters.