Jordan Spieth keeps challenge going amid concern for Jason Day

The sight of one of his fellow contenders slumping to the ground, as happened to Jason Day on his finishing hole, wasn't what Jordan Spieth had bargained for. But, then, as some players whinged and moaned about the tainted colouring of the greens, and of bumpy lines and inconsistent speeds on their putting at this 115th edition of the US Open at Chambers Bay, the plight of the prone Australian brought its own kind of perspective.

“I have got vertigo, I will be okay,” said Day, as the player was assisted out of the recorders’ hut by two medical assistants on the way to hospital. Yet, there was a greater concern for his well-being given that Day had undergone a series of MRI scans on his head, back and his neck in recent months following a number of similar incidents.

Spieth later remarked: “I was walking with him, the next thing I know I turned around and I think he got dizzy and slipped and fell. So at that point, how can we help him out and kind of clear the scene and try and keep the cameras off and let him just rebound from being dizzy. That’s all it was, I think. I don’t think it was a slip off of the ground. I think it was maybe a little dehydration or something. I’m not really sure. He didn’t mention much after the round. We were trying to look out for him.”

On a day which started with grey cloud cover and a gentle breeze, Spieth – chasing back-to-back Majors having won the Masters in April in hugely impressive fashion – again showed his pedigree. He shot a second round 67 to reach the midpoint of the championship on 135, five under par, to claim the clubhouse lead.

And Shane Lowry, despite suffering the wrath of the course with a double-bogey on the 14th hole where he putted off the vicious green into a bunker, showed his own fortitude with a finishing birdie on the 18th, ranked the toughest hole of all, for a 70 that left him on 139, one under, and very much in the hunt. It marked Lowry's first cut in what is his third US Open.

On another day, that double bogey might have seen the wheels come off. But Lowry’s patience was admirable, and he stuck to the task. Patience, not a commodity that has always sided with him, proved vital. “I felt in control of myself all day yesterday and today, it feels good to be here and feeling the way I’ve felt. My emotions, everything, and I just need to keep that in tact,” said Lowry.

His finish on the 18th was sublime, hitting a 7-iron approach from 182 yards to within inches of the cup for a rare birdie on a hole – reduced to a Par 4 – that played as the toughest on the course.

“I done well to come back (from the double). I’d chances on 15, 16, a great par putt on 17 from 10 feet, then went on to birdie the last. One of those days I am happy with, it could have been a bit better but I am in a great position for the weekend. My game feels very good,” he said.

Certainly, as his top-10 finish in last year’s British Open confirmed, Lowry has the mentality for the big occasion. “There’s a lot of golf to be played yet. If I can just go out, keep doing my own thing, I am driving the ball, my iron play feels good. You never know what might happen come Sunday,” said Lowry, happy to have a late tee-time and his sights on the likes of Spieth four shots ahead of him.

Spieth also had a double bogey in his round, on that 18th hole, his ninth, but bounced back with a birdie on the first and kept his focus until the end. The only time his focus drifted was to observe the prone Day, who feel to the ground on the ninth – their finishing hole – with his latest episode of a vertigo attack.

Day, who was attended to by medical personnel on the hole, gingerly regained his feet and finished the hole – with a bogey for a 70 that left him on 138, two under – before being brought to the recorders and onwards to hospital for observation and treatment.

Prior to the championship, Day – who was forced to withdraw from last year’s WGC-Bridgestone Invitational due to dizzy spells – had remarked: “I had three sleep studies done and everything came back negative . . . And everything came back negative. So I have no idea what that was, other than I just may have been exhausted.

“I was training so hard coming into tournaments and then on top of it I was doing practice, playing competitive golf and then trying to balance that with family as well. It’s just a full-time kind of gig there. And I think I just ran out of gas. I wasn’t feeling good, so I had the shakes and the tingling up my arms. And the loss of energy and strength was probably caused by that.”

Tiger Woods bowed out after a second round of 76 left him on 16 over, one shot ahead of Darren Clarke, who suffered an 80 in his second round .