Murray beat Uzbekistan’s Istomin 6-3 7-5 in the evening session when the heat was cooler.
Playing in the final session of day six, second seed Murray beat world number 76 Istomin to make the third round.
That came despite ending up serving with a rogue ball from the women’s event in the second set which actually saw him broken on serve before he broke straight back to set up a clash with Bulgaria’s Grigor Dimitrov.
“The women’s balls are very different from the men’s balls,” he said.
“They’re much quicker, smaller, livelier, and 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.”