Defending champion Katie Boulter edged out Harriet Dart in a marathon all-British tie to reach the second round of the Nottingham Open.

Opening her grass-court season, third seed Boulter won 6-7 (5-7) 6-4 7-5 in a contest lasting three hours and 13 minutes.

But the enthralling match was tainted as a frustrated Dart repeatedly argued with the chair umpire over what she believed to be incorrect line calls.

Their dispute reached its height during a change of ends in the second set, after a ball from Boulter was called out but overruled by umpire Kelly Rask.

In response, Dart offered a 50,000 bet that the ball in question was out.

"The ball is so far out, this is embarrassing. You're embarrassing yourself. You should be embarrassed," the 27-year-old told Rask.

After asking to speak to the tournament referee, Dart then accused Rask of "threatening" her with a code violation.

Speaking after the match, Dart said the line calling was "pretty appalling" and called for technology to be used across the sport.

On her dispute with Rask, she said: "Give me a code violation or don't. I think she was a bit embarrassed by the situation. We are all professionals here.

"I have played so many tennis matches in my career and this one was a little bit disappointing with some of the things. I think she can also reflect on that."

British number one Boulter will play Viktorija Golubic of Switzerland or Canada's Rebecca Marino in the second round.

The 27-year-old's victory in Nottingham 12 months ago was her first WTA title.

"That was an absolute battle," Boulter, ranked 30th in the world, said of her contest with Dart.

"[Dart] is an incredible grass-court player. I tried to do the best I could because she was playing seriously good stuff.

"I would have taken a much easier win, that's for sure. I'm not sure I've seen a three hour, 13 minute grass-court match. I'm not sure that's possible."