Macartney walked out to bat for the touring Australians on the first day of the tour match against Nottinghamshire on 25 June 1921. By stumps he had 345 in his name from less than four hours' batting, and the innings was over: caught behind by W.G. Quaife off the bowling of Tom Richmond. The total had taken him 232 minutes and contained 47 fours and four sixes. He reached 100 in 116 minutes, 200 in 161 minutes, and 300 in 205 minutes.
The Trent Bridge attack was no village standard — it included Fred Barratt, Sam Staples and Richmond, all county professionals — but Macartney drove and pulled with the freedom of a man playing on a beach. Wisden recorded that 'his footwork was so quick that he made medium-paced bowlers look slow', and that he twice in the same over took a ball from off-stump and pulled it for six over square-leg. Notts captain John Carlin shifted bowlers and fielders constantly; nothing worked.
The 345 was at the time the highest score made in England by a touring batsman, the highest individual score at Trent Bridge, and the most runs ever made in a single day's play in first-class cricket. The single-day record stood until Brian Lara's 390* on the way to 501* in 1994. The figure would also remain the highest score by an Australian in England until 2003.