Leading article: A star is born

It's reasonable to suppose that theatre-goers who scrambled for first-night tickets for The Children's Hour, Lillian Hellman's classic 1934 play about two women accused of having a lesbian relationship, did so chiefly for the prospect of seeing live on stage two of the biggest screen stars of the moment, Keira Knightley and Elisabeth Moss.

Knightley entered British affections nearly 10 years ago when, as a 17-year-old, she gave a winning performance in Bend It Like Beckham, and she has remained there ever since. With Moss – integral to the success of the TV series Mad Men – it was a case of bringing a very American kind of glamour to the West End.

Yet when the reviews appeared after Wednesday's first night, it was neither Knightley nor Moss who was uppermost in the critics' minds. That honour went to the almost unknown Bryony Hannah as the trouble-making student Mary Tilford. While opinion was divided on the two big names, there was only one view about Hannah's performance. "A fantastic find", "utterly compelling", and "steals the show" were among the accolades.

A star, it seems, is born. And audiences who knew they would exult in saying, "I saw Keira Knightley and Elisabeth Moss" might be even more thrilled to report that they saw Bryony Hannah. A litte upstaging goes a long way.