However, the American has insisted that he was fortunate to post such a good score in testing conditions at Royal Birkdale.
The 23-year-old is quoted by BBC Sport as saying: "I give myself a B grade today. I got pretty frustrated through the turn, hitting it into pot bunker after pot bunker and squeaking out pars somehow.
"I didn't get everything I could out of yesterday's round and I got more than what I deserved today."
Spieth has made the cut on each of his five appearances at The Open, with his best finish currently a share of fourth at St Andrew's in 2015.