An eagle on the 15th was the highlight in a second-round 69 which moved the American to six-under at halfway.

Spieth says a weather break in the middle of his round helped him recover composure.

"I give myself a B grade today. Which is giving myself some credit, I got pretty frustrated through the turn there in the middle of tthe round, just hitting it into pot bunker after pot bunker, sqeaking out par somehow.

"I thought we did a really good job once that horn blew, and it could have been better timing where I could sit back and almost play the last 8-holes as a new round."

Matt Kuchar leads the chase at four-under with Ian Poulter and US Open champion Brooks Koepka both three-under after 36 holes.

Rory McIlroy's second-round 68 has got him back into contention at one-under.

The other Irish players all missed the weekend.

Padraig Harrington, winner at the venue in 2008, ended one shot outside the cut at six-over.

2011 champion Darren Clarke closed eight over while Shane Lowry finished 10-over.

Meanwhile, Alfie Plant is set to win the silver medal as the Open's leading amateur after making the cut at Royal Birkdale.

The 25-year-old European Amateur champion from Bexleyheath shot a three-over-par second-round 73 to make it to the weekend on four over.

As the only amateur to survive the first two rounds, he will secure the silver medal if he completes all 72 holes of the tournament.