Australians Greg Chalmers and Aaron Baddeley are tied for fourth at the PGA Tour&aposs Humana Challenge after the first round on Friday morning (AEDT), one shot behind the joint leaders. Chalmers and Baddeley both shot eight-under 64s to be well in the mix at La Quinta, California, with each of them holing multiple eagles in their opening 18 holes on a good day for scoring. Baddeley is looking to add to his three PGA Tour titles, while Chalmers is chasing a maiden trophy on the prestigious US circuit. The pair sit a solitary stroke behind American trio Roberto Castro, Jason Kokrak and James Hahn, with last week&aposs Sony Open winner Russell Henley sitting level with the Australians just off the pace. Also on eight under is American Doug LaBelle II, ahead of a group of nine tied at seven under – all from the United States – including Jeff Maggert, Daniel Summerhays, Michael Bradley, Ricky Barnes, Charley Hoffman, Cameron Tringale, Ryan Palmer, Jerry Kelly and Patrick Cantlay. In his first tournament of 2013, four-time major winner Phil Mickelson shot an underwhelming even-par, mixing three birdies with a bogey and a double bogey. The next best of the Aussie contingent is Stuart Appleby on five under, going bogey-free on the La Quinta Country Club course – one of three in use at the tournament. Alistair Presnell sat atop the leaderboard through his front nine – when he went six under via six birdies – but slipped to a tie for 48th after his back nine which saw him finish the day on four under. Also on four under were compatriots Matt Jones and Robert Allenby, with Geoff Ogilvy, Scott Gardiner (both two under), Steven Bowditch (one under), Cameron Percy and John Senden (both even par) the other Australians in the field.