Steve Smith was forced to retire hurt on the verge of another, after copping a sickening blow on the back of the neck.
What has already been an enthralling battle between the pair, Smith has been hit square on the arm, and winced and grimaced as he struggled to grip the top of the bat in the overs after.
Then, after Archer bowled in the fastest recorded in English Test history (an average speed of 92.79 mph), he got a delivery to rise steeply. Smith was caught between the ducking and playing a shot, turned his head, and was hit by the back of the helmet.
A hush over the Lord's, as inlookers waited for movement. Eventually, Smith was able to rise and move across the crease, before being escorted off the field.
If that is the case, it would be the first time in Test history that a concussion substitute would be called.
More to come.