Paris - Andy Murray vented his frustration at a lack of consistency from umpires after receiving two time violations in Wednesday's win over Kei Nishikori at the French Open.
World number one Murray reached the last four at Roland Garros for the fifth time with a 2-6, 6-1, 7-6 (7/0), 6-1 win over Japanese eighth seed Nishikori.
But he was twice penalised by Carlos Ramos for taking too long between points, losing a first serve following a repeat offence early in the second set.
The incident appear to fire up Murray as the Briton ran away with the second set, but he expressed his dismay at the way the rules are applied.
"It's possible that I'm playing too slow. I don't know, because we don't have the clock on the court so it's impossible for us to tell," said Murray.
"We can't tell, as players, how long we are taking. You're allowed 20 seconds here. The rest of the year it's 25 seconds.
"How the players are supposed to know that in their head when we're playing at one speed throughout the whole year, and then you show up at the slams, you're expected to speed up by 5 seconds. It's a pretty long time."
Rafael Nadal took issue with Ramos earlier in the tournament for treating him like a "machine" and suggested he was being unfairly targeted to speed up play.
"I think if someone is intentionally slowing a match down they should be punished for that, but it's a rule that is going to be challenging regardless of whether there is a clock on the court or not," added Murray.
"It's difficult because the consistency is not there."