Spieth took a five-stroke edge into Saturday after setting a 36-hole scoring record at Augusta National with a 14-under 130, having made 15 birdies and just one bogey over the first two days.
The 21-year-old Texan nearly became the youngest Masters champion a year ago, leading by two strokes on the final day before fading down the stretch to finish in the runner-up spot behind Bubba Watson.
Now, Spieth wants to finish the job — and he's certainly got history on his side.
The five-shot lead heading to the weekend matched the largest ever at the midway point of the tournament, joining Herman Keiser in 1946, Jack Nicklaus in 1975 and Raymond Floyd in 1976. They all went on to capture the green jacket.
"No scoreboard watching," Spieth said. "Just keep my head down and set a goal for myself."
The birdie-friendly greens didn't get any tougher after overnight rain dampened the course.
The early starters took advantage, putting up some impressive scores.
Not giving up on completing his career Grand Slam, Rory McIlroy followed up a 31 on the back nine Friday by shooting 32 on the front side Saturday. He rolled in an eagle at the second hole, followed by back-to-back birdies at Nos. 8 and 9. He was 6 under overall and eight shots behind as Spieth teed off.
Tiger Woods, who won the last of his 14 major titles nearly seven years ago, ripped off three straight birdies starting at No. 2 to get within nine shots of the lead. He nearly made a hole-in-one at the par-3 fourth, his tee shot stopping less than a foot from the cup for a gimme 2.
Ian Poulter posted a 5-under 67. Rickie Fowler was 5 under for the day until his first bogey at the 14th stymied his momentum a bit.
Spieth played in the final group with perhaps the most surprising player of the tournament, Charley Hoffman.
A 38-year-old journeyman who had only qualified for the Masters one other time, back in 2011, Hoffman opened with a pair of rounds in the 60s for a 9-under 135 that would've been good enough for the 36-hole lead most years.
Not the way Spieth was playing.
After starting with a 64 — the lowest opening round at the Masters in 19 years — he made Friday's 66 look downright easy. Spieth's most challenging putt to save par was about 7 feet. He would have gone even lower if not for misses from inside 10 feet at the ninth and 18th holes.
"It's a long, long way from being finished," said Ernie Els, who began the third round nine shots back. "A lot of work still to be done, so we'll see. But he's very, very impressive."
Justin Rose, Dustin Johnson and Paul Casey were seven shots off the lead, with Phil Mickelson joining McIlroy another stroke back.
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