Miami Open: Andy Murray and Heather Watson progress

Andy Murray's latest win was not entirely straightforward due to the balls he was using

Britain's Andy Murray and Heather Watson both progressed at the Miami Open on a day when players struggled in the heat.

Murray played in cooler temperatures as he beat Uzbekistan's Denis Istomin 6-3 7-5 in the evening session.

Watson had earlier fought back to beat Belgian Yanina Wickmayer 3-6 7-5 6-3 over two and a half hours.

Fellow Briton Aljaz Bedene was forced out with a wrist injury, while Jamie Murray lost in the doubles.

Murray wins despite rogue ball

Having waited until the final session of day six to play his first match, second seed Murray saw off world number 76 Istomin in one hour and 38 minutes.

There was a moment of confusion in the second set when Murray found himself serving with a rogue ball from the women's event, and duly dropped serve.

"The women's balls are very different from the men's balls," he said.

"They're much quicker, smaller, livelier. When you're just about to serve at break point down, you don't want to be using a completely different ball. So I was just a bit frustrated with that."

Murray broke straight back in the following game on his way to setting up a match against Bulgarian 26th seed Grigor Dimitrov in round three.

Watson thrives in the heat

Heather Watson's performance is set to see her world ranking of 69 rise

The British number two battled superbly to see off Wickmayer, ranked 22 places higher at 47, and reach the fourth round in Miami for the first time.

Watson saved five break points across her final two service games in the second set to level the match and served impressively in the decider.

The combination of heat and humidity was so testing the players required a change of clothing before the final set.

"We actually went to the porta-potties - that's where the referees took us - and we both had to get changed in there because we were just drenched," said Watson, who plays Romanian fifth seed Simona Halep next.

And on a day when Spain's Rafael Nadal had to retire because of the extreme conditions, Watson was back out for a doubles match later in the day.

"I've surprised myself," she said afterwards. "I'm actually feeling fine right now, but when I get to my hotel and lie down for a second, I'm probably going to pass out!"

Bedene and Jamie Murray bow out

Three days after his appeal to represent Britain in the Davis Cup was rejected, Slovenia-born Bedene felt the disappointment played a part in his Miami exit.

Bedene trailed Spanish 17th seed Roberto Bautista Agut 7-5 2-2 when he felt he could no longer continue.

"It's just consistent pain in the wrist," he said. "It's been going on for 10 days now.

"Obviously the mental part has a lot to do with it. I'm hoping all this nonsense I went through had something to do with the wrist."

Jamie Murray had hoped to clinch the number one spot in Miami, having missed a chance in Indian Wells last week, but must now rely on other results going his way.

Murray and Soares took the first set but went down 3-6 6-3 10-7 to Rajeev Ram and Raven Klaasen.