The Swede, who lost to defending champion Lee Westwood in a play-off last year, carded an opening 66 to finish one of the past.
World number two Westwood, three shots further back, made a steady start but remains ‘s 13/2 favourite.
Padraig Harrington (40/1 William Hill) finished level par, five shots behind leader David Mathis, whose six birdies ensured he has a one-shot lead over the field and can be backed at 28/1 with bet365.
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St Jude Classic – First round leaderboard (US unless stated)
-5: D Mathis -4: J Merrick, K Blanks, K Kisner, R Karlsson (Swe), C Knost -3: K Bradley, F Gomez (Arg) Selected others: -2 R Goosen (SA) -1 L Westwood Level P Harrington (Ire) +8 S Garcia (Sp)