Kiwi No 1 Danny Lee clawed back to square his World Golf Championship match on the second nine against Charl Schwartzel before slipping away once more and losing 1 down to the former Masters champion.

Lee was never in front at the Austin Country club in Texas as the opening games began in the five day event.

"Danny made a really good comeback, made a few birdies on the back nine," said Schwartzel.

"Then it felt like we both started playing a little scrappy and were just really hanging in there by the skin of our teeth. I'm just happy that I hit some good shots coming in."

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Meanwhile Jason Day suffered a back injury in his opening round win over Graeme McDowell, potentially putting his Masters tilt in doubt.

The world number two was three-up after 14 holes when he winced in pain hitting a tee shot on the 15th hole, straining something in his lower back and suffering nerve pain.

He was able to scratch out halves in the next two holes to win the match 3 and 2 but was in serious discomfort, struggling to walk.

The Masters are just two weeks away.

In other action, Jason Dufner beat Rickie Fowler 2 and 1, Byeong-Hun An halved with Scott Piercy, Brandt Snedeker beat Charley Hoffman 2 and 1, Thongchai Jaidee beat Paul Casey 2 and 1, Kevin Kisner beat Soren Kjeldsen 2 and 1 and Rafa Cabrera Bello beat Hideki Matsuyama 1 up.