Labuschagne rides emotional rollercoaster as Ashes super sub

Australia's Marnus Labuschagne admitted experiencing a rollercoaster of emotions when he became Test cricket's first concussion replacement.

Labuschagne came into the Australia team on the fifth day of the second Test against England at Lord's after Steve Smith was diagnosed with a delayed concussion.

Smith had been hit on the head by Jofra Archer the day before and it took just two balls on Sunday for the England paceman to floor Labuschagne with another fierce bouncer to the helmet.

The 25-year-old was put through the same on-field concussion testing as Smith 24 hours earlier, but came through. He went on to top score with 59 as the tourists held on for a draw.

"Personally, being out there is probably less nerve-racking than being off the field," Labuschagne said.

"When he got hit, I had a bit of a sick feeling, you're kind of helpless. But when you're out there you're in the contest and the adrenaline is rushing pretty much all you're doing is trying to watch that ball.

"When you're off field and your hands are tied...it's a little bit of a shock to the system. But when you're out there, it's all guns blazing."