The veteran Swede began working with Edmund last autumn and in their first grand slam together the 23-year-old has reached his maiden quarter-final.
He will take on third seed Grigor Dimitrov on Tuesday, and anyone who has not seen Edmund play for a few months may be taken aback by the Yorkshireman’s new demonstrative nature.
Naturally an introvert, Edmund is learning to embrace the gladiatorial nature of professional tennis, with impressive results.
Rosengren said: “I always believe it has to be fun out there, you have to enjoy the challenge, it’s not always about winning or losing. Sometimes you can be part of a great match but you lost.
“So we talked about it a lot, but at the same time he can’t (pump his fist) because I told him to. It has to come from his heart. I’m very happy to see that he’s happy out there and is not afraid of showing his emotions. I 100 per cent believe it helps him in his game.”
Rosengren’s emotions are always evident, with the 57-year-old – who is known as Fidde – a live-wire presence in the stands.
“I’ve been sitting there for 30 years,” said Rosengren, who has coached five top-10 players, including Swedes Robin Soderling and Magnus Norman.
“I’m always into it because I love my work. This is the party time. I have worked with so many great players and so many great characters and this makes my job so fantastic. It makes me jump off the bed every morning to have the privilege to work with different kinds of people.
“And if I can improve Kyle as a person also, then it’s almost even better because he has a life afterwards.”
Edmund made steady progress up the senior rankings after a fine junior career but trod water in his results in 2017 and split from previous coach Ryan Jones before Wimbledon.
He trialled Rosengren and British coach Mark Hilton, who had guided Dan Evans into the top 50 prior to his doping suspension, before deciding to hire them both.
The priority during the off-season was changing Edmund’s serve, which had not been as big a weapon as it should have been, and harnessing the power of his forehand.
Asked for his first observations of Edmund, Rosengren said: “That’s a a hell of a forehand, one of the best forehands out there, but at the same time you have to use the forehand right. For me it was a little bit like Kyle learning to take the right club out of the bag. Sometimes he used the driver on the putting green.
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“One main thing I saw was his service level was very up and down so we said we have to try to change the serve. I think everyone who has been watching him the last weeks can see how he raised his serve level. I’m very happy, and also that Kyle wanted to change.”
The other thing holding Edmund back was his failure to win close matches. In 2017, he played 25 deciding sets and won only seven of them. This season already he has won four out of five.
The victory over US Open finalist Kevin Anderson in round one in Melbourne, the biggest scalp of his career, leaps out but Rosengren has been even more impressed with his following three wins against Denis Istomin, Nikoloz Basilashvili and Andreas Seppi.
He said: “Everybody told me about this. You have to take away the pressure. I’ve been amazingly happy. He showed me so much courage and it’s so great to see. I tried to tell him, ‘stay on the court, enjoy the moment’, so he really feels like he’s a great player, because he is a great player.”
The one deciding set Edmund has lost this season came against Dimitrov in Brisbane, when he matched the Bulgarian before turning his ankle late on. Their other previous meeting in Washington last summer also went the distance.
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