Johanna Konta’s defence of the Miami Open title was ended by a 7-5 1-6 2-6 defeat to Venus Williams in their fourth round match in Key Biscayne.
The British number one will drop from 14th to outside the world top 20 as a result of a loss that ends her recent return to form.
Williams, playing in the tournament for the 19th time and reaching the quarter-finals for a 13th occasion, was outstanding after coming off worse in a wobbly opening set and the 37-year-old was cheered on by the crowd.
Konta made a roaring start by breaking in the first game of the match and she almost repeated the feet in a marathon third lasting almost 11 minutes only for Williams to recover.
The score was levelled in the sixth due to a mixture of Williams’ power and the collapse of Konta’s serve and the Briton was told to “hang in there” during a pep talk by her coach Michael Joyce.
The words were heeded as Konta dug in to save set point before recalibrating her serve in the nick of time, wining the decisive game with some classy shots.
The Sydney-born 26-year-old’s momentum halted abruptly, however, as Williams raced 3-0 ahead in the second set and, when Konta double faulted in the seventh, her fate was effectively sealed.
A lengthy spell of treatment preceded the third set, but the lower back injury failed to prevent Konta from holding her own in the early stages before Williams pulled clear, clinching the match through an unforced error.
Elsewhere, Spanish third seed Garbine Muguruza followed Konta out of the tournament, losing 3-6 4-6 to Sloane Stephens, while her fellow seeds Karolina Pliskova and Elina Svitolina progressed to the quarter-finals.