Spieth, who was second on his debut in 2014 and claimed a first green jacket with a record-breaking performance 12 months ago, carded six birdies and no bogeys despite swirling winds on the opening day at Augusta National.
That gave the 22-year-old a two-shot lead over Lowry and New Zealand’s Danny Lee, with Paul Casey, Justin Rose, Ian Poulter, Sergio Garcia and Soren Kjeldsen all a shot behind on three under.
Rory McIlroy, who is seeking a first Masters title to complete the career grand slam, was a shot further back alongside Danny Willett, with McIlroy dropping shots on the 16th and 18th and Willett making his only bogey of the day on the last.
World number one Jason Day was a shot off the lead when he raced to the turn in 31 with an eagle and three birdies, but dropped five shots in his last four holes - including a triple bogey on the 16th - to finish level par.
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Spieth, who is looking to become just the fourth player after Jack Nicklaus, Nick Faldo and Tiger Woods to successfully defend the year’s first major championship, led from start to finish after an opening 64 last year and was quickly into his stride with birdies on the third, sixth and eighth.
The world number two, who set records for the highest number of birdies (28) and lowest 36 and 54-hole totals in Masters history last year, also birdied the 10th, 13th and 18th, but was equally pleased to scramble pars on the 11th, 12th and 16th.
“I would have signed for two under today and not even played the round, knowing the conditions that were coming up,” said Spieth, who is a record 29 under par for his nine competitive rounds in the Masters. His position after each of those rounds reads 12-3-1-2-1-1-1-1-1.
“I got a lot out of the round with what I felt like was kind of average-ish ball-striking. I got the most I could probably get out of my round today.
“I think the round today may have been better than the first round last year because of the conditions.”
Meanwhile, Four-time major winner Ernie Els suffered a nightmare start taking anincredible six putts on the opening hole.
Els, who thought he had conquered the dreaded “yips” earlier this season, looked set to save par on the 445-yard par four after missing the green with his approach but hitting an excellent pitch.
However, the 46-year-old missed from three feet and needed five more attempts to get the ball in the hole, the last two being taken with one hand as his frustration understandably soared.
The resulting quintuple-bogey nine is the highest score on the hole in Masters history, surpassing the eights taken by Olin Browne.