Jason Day opens up five-shot lead midway through day two at Bay Hill

Jason Day opened up a commanding lead at the Arnold Palmer Invitational after he followed his opening 66 with a flawless 65 in perfect scoring conditions at Bay Hill.

Day birdied four of his last seven holes to set a daunting clubhouse target at 13 under par, earning him a five-shot advantage over nearest challenger Jamie Lovemark halfway through the second day.

The Australian started at the 10th and followed a pair of pars with a neat pitch to inside three feet at the long 12th to set up his first birdie of the round, and he added another at 16 after narrowly missing an 18-foot putt for eagle.

Day then rolled in a huge 35-footer for birdie at the 17th, and he picked up another shot at the third, where his 91-yard approach almost spun into the cup for an eagle-two.

The world No 2 carded another birdie at five and he got up and down from a greenside bunker for another gain at the next, and he capped a superb day's work in thrilling style as he drained another birdie putt from just inside 40 feet on the ninth green.

"It was great. I felt like I couldn't do anything wrong out there," said Day, whose halfway score was just one outside the tournament 36-hole record. "I was driving it nice and driving it really long. I had several shots to hit a lot of greens and I putted fantastic.

"To hole 125 feet of putts was fantastic and the putts on nine and 17 definitely helped that along. But I was very, very pleased. My goal was to try and stay patient but still aggressive and it worked out over the last two days."

Lovemark emerged as Day's closest rival from the early starters as he returned a second consecutive 68 featuring five birdies and a lone blemish at the seventh - his 16th - to close on eight under.

Paul Casey was a shot further back as he continued his encouraging recent form with a 69, although he took the gloss off an excellent inward nine with a bogey at the last.

The Englishman dropped a shot at the first after pulling his drive into the rough on the left, but he responded with a 15-foot putt for birdie at the third before getting up and down for another at the long fourth.

Casey took another step back at the ninth when he missed a four-footer for par after bunkering his approach, but he reeled off three birdies in four holes after the turn and two-putted from distance for another at 16.

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But a blocked drive and a pulled second cost him a shot at the last as he slipped to seven under, while South Korean veteran KJ Choi (70), Jason Kokrak (68) and David Hearn (67) were all a shot further adrift in the clubhouse.

But Matt Every, champion for the last two years at Bay Hill, looked certain to miss the cut after a disappointing 74 which included a triple-bogey seven at the 11th - his second hole of the day.

Every finished on one over, a shot outside the projected cut mark, while Luke Donald will certainly have the weekend off after an erratic 75, closing with a double-bogey six at the last when he put his second shot into water.