Britain's Sonay Kartal says it was "one match too many" as a lower back injury forced her retirement from a fourth-round Indian Wells match against world number three Elena Rybakina.

Receiving physio treatment between games, Kartal lost the first set to the Kazakh 6-4.

Then, in clear discomfort as she trailed 4-3 in the second having been broken when she stretched for a return, she made her way to the net to shake hands.

The 24-year-old had battled the problem through the tournament and said she had to "pull the plug" on Wednesday as the pain got more intense the further the match went on.

"As athletes you are super in-tune with your body, and I've had it pretty much the whole event, so I kind of knew that I could keep pushing," Kartal told BBC Sport.

"But today it was unfortunately one match too many.

"[I played] a super-tough opponent, so you need to be at your best. I was far from that but still managed to make it competitive."

Kartal, ranked 54, had become the first British woman to twice reach the fourth round in California.

Rybakina will play fifth seed Jessica Pegula in the quarter-finals after the American overcame Belinda Bencic 6-3 7-6 (7-5) to secure her first victory in five meetings between the pair.

World number two Iga Swiatek reeled off 10 consecutive games in a 6-2 6-0 victory over Czech 13th-seed Karolina Muchova.

Pole Swiatek, chasing a third Indian Wells title, will face ninth seed Elina Svitolina in the quarter-finals. The Ukrainian was leading Katerina Siniakova 6-1 1-1 when her opponent retired with an injury.