British teenager Andy Murray passed his first test under new coach Brad Gilbert, defeating Ramon Delgado in straight sets at the Legg Mason Classic on Wednesday.
Murray struck 13 aces and six double faults in the 6-4, 6-3 second-round triumph over Paraguay's number one.
The 44-year-old Gilbert, who coached Andre Agassi and Andy Roddick to the world's top ranking, has been in the Murray camp for less than a week.
"He gave me a C for my performance," said the 19-year-old Murray. "He was pleased that I managed to get through. It's hard for him to do really good work the first couple of weeks."
Murray conceded he has "definitely played better matches" but said he had not practised on hard courts in several months and had a tough time negotiating the steamy Washington weather.
The Scotland-born Murray repeatedly looked in the stands at Gilbert, who was signed last week by Britain's Lawn Tennis Association to fortify the nation's sagging tennis fortunes.
"All players tend to look at their coaches, especially in important situations" said Murray. "It's not so much for tactics, it's more to look at a familiar face, to someone you trust and respect."
Murray led 5-2 in the second set but failed to close out the match on his serve, drawing criticism from Gilbert.
"He played a couple of loose games and there were a few double faults," said Gilbert, who said the 6-foot-1, 68 kgs Murray needs to get stronger and in better shape. "He needs to get better in a lot of areas.
"Everyone thinks I'm a magician, I just touch him and he can become great. I believe in hard work, dedication, desire and just being methodical."
The temperatures in Washington were in the 38 Celsius range causing problems for many of the players.
"Pretty much everyone is struggling with the weather," the British number one said.
"It plays a big factor in all of the matches. You have to maybe finish the points a bit quicker than normal.
"It is so hot out there that if you're defending all of the points it's tough to catch your breath because it's so humid."