Australia's Jason Day claimed a one-shot lead at the halfway stage of the Masters, but all the headlines were about two players at the opposite ends of the age spectrum on a dramatic day at Augusta National.

In the last group out, Day carded a 68 to finish six under par, one shot clear of compatriot Marc Leishman and 53-year-old former champion Fred Couples.

And by failing to birdie the 18th, Day ensured Chinese teenager Tianlang Guan made the cut on four-over under the 10-shot rule, despite the 14-year-old earlier being penalised a shot for slow play.

Argentina's Angel Cabrera, the 2009 champion, was two off the lead alongside American duo Jim Furyk and Brandt Snedeker after storming home in 31 with five birdies in his last six holes, while English trio David Lynn, Lee Westwood and Justin Rose were another stroke back on three under.

Rory McIlroy was the only member of the Irish quartet to make the half-way cut after shooting an impressive two-under 70 to sit four shots off the lead going into the weekend.

McIlroy had an eagle on the eighth and birdie on the 18th in his round of 70 to lie two under, the same score as two-time winner Bernhard Langer after the 55-year-old completed a second consecutive 71.

Graeme McDowell missed the cut by one shot with a five over finish, while Padraig Harrington finished on nine over with amateur Alan Dunbar finishing on 16 over par.

Jason Dufner, KJ Choi, Adam Scott and Tiger Woods were also three under, 14-time major winner Woods dropping two shots in the last four holes by three-putting the 18th after seeing his pitch to the 15th hit the pin and bounce back into the water.

Couples, who claimed his only Green Jacket in 1992, also shared the lead with Dufner at the same stage last year but shot 75 on Saturday and eventually finished 12th.

"I would like to have another run," Couples said. "Last year both Jason and I struggled right off the bat and we really were a non-factor on Saturday and that was not really much fun.

"Hopefully tomorrow will be a little different and I will play well and have a shot at Sunday. That's my goal, but it is hard. I'm not going to kid you. I'm really tired.

"Am I good enough to play four good rounds in a row on a course like this? It didn't happen last year. I did tee off Thursday with the idea of playing well, and now it's Friday afternoon late. I'm surprised, but I'm not going to freak out over it."

Guan, the youngest player in Masters history, added a 75 to his opening 73 to finish four over par, but only after being controversially handed a one-shot penalty for slow play.

The rules state that players will be told when they are out of position on the course, then advised they are being put on the clock and if they subsequently receive two "bad times", are liable to be penalised.

Guan was warned on the 10th, started being timed on the 12th and then took too long over his second shot to the 13th and approach to the 17th.

Speaking to ESPN, Guan said: "I respect the decision. This is what they can do. I think they should do it with respect to everybody."

World number one Woods, who shared the lead before a back nine of 38, said of his bad luck on the 15th: "I was pretty pissed. Looked like I was making birdie and now I have to struggle not to drop two shots.

"It was a good six but I played really well today and the round should have been in the 60s."

Earlier in the day, Lynn added a 73 to his opening 68 in his third career major, while Westwood and Rose both returned 71s.

Lynn, who had two bogeys and just one birdie on the 18th, said: "I was just grinding out the pars. I actually had quite a few chances on the back nine, so to finally finish with a birdie I hit a fantastic shot into the last to about six feet.

"As we can see by the numbers on the scoreboard, nobody is running away with it, so boring is good."

Westwood, who opened with a double-bogey six on Thursday, said: "It was a solid day and I did what I needed to in the conditions. It feels like the sort of week where nobody is going to run away with it."

Overnight joint-leader Sergio Garcia was 10 shots worse than his opening 66 to also finish two under, while American Dustin Johnson was the only player to reach seven under after 13 holes of his round, only to play the last five holes in six over par.

Defending champion Bubba Watson scraped into the weekend on four over after a 73, but Ian Poulter crashed out on seven over.