Andy Murray got Great Britain off to a winning start in their Davis Cup tie against Croatia but the hosts levelled things up at the end of day one in Umag.
Murray eventually came through with relative ease against 16-year-old Borna Coric, winning 6-3 6-0 6-3, but had to work hard early on with the first set containing a 57-shot rally.
British number two Dan Evans - ranked 149 in the world - was then outclassed in his rubber against world number 35 Ivan Dodig, losing 6-3 6-2 6-3.
"The first five or six games were tough," Murray told Eurosport.
"I wanted to try and make the points long and make it challenging for him physically, which I did, but I missed a few shots early on, maybe playing with too much spin.
Once I got the break, I then won quite a few games in a row, but lost concentration at the start of the third. It's okay. It will get better.
"But he was solid. He didn't make many mistakes, fought for every point, and when he gets physically stronger he is going to be a very tough player."
US Open junior champion Coroc was making his Davis Cup debut as a stand in for Marin Cilic, who was unavailable.
Murray, making his first Davis Cup appearance for two years, appeared to be suffering some back pain in the third set.
"My back is a little bit sore - the change of surface is difficult, but after a couple more matches I'll have some time to rest, so let's just get the win this weekend," said the world number three.
Evans, who recently broke into the world's top 150 for the first time after reaching the US Open third round, struggled against a far superior opponent.
Saturday will see the doubles contested with the reverse singles on Sunday, and Murray is expected to pair up with Colin Fleming tomorrow.
The tie's winner will advance to the elite World Group, a level which Britain have not reached since 2008.
Reflecting on the opening day's action, GB captain Leon Smith said: "Not a surprise after day one, it is where we expected and both favourites won.
"Whoever we put out to play tomorrow, I'm confident we will do well and as I said before, it will be the key rubber."
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