Murray, a three-time semi-finalist, had needed two five-set matches and three days of play to get to the last 32.

But on Friday the 29-year-old needed just a shade under two hours to beat 6ft 11in (2.11m) Karlovic 6-1, 6-4, 7-6 (7/3).

It was his seventh win in seven matches against the 37-year-old as Murray goes on to face either John Isner of the United States or Teymuraz Gabashvili of Russia.

“Especially at the end it was very close. I got off to a quick start and against someone like Ivo that’s very important,” said Murray.

“I was glad to win that tiebreak at the end.”

Canada’s eighth seed Milos Raonic overcame a left hip injury to defeat Slovakian lucky loser Andrej Martin, the world number 133, and reach the last 16 for a second time. AFP

In only her fifth Fed Cup appearance, world number four Sharapova won both singles matches, beating 11th-ranked Karolina Pliskova in straight sets on Saturday and sixth-ranked Petra Kvitova in a three-set thriller on Sunday.

“Personally it’s an incredible achievement for me because I’ve never been in a Fed Cup final and I won two of my matches,” Sharapova said.

After winning five Grand Slam titles, Sharapova is still seeking two other global trophies — the Fed Cup and Olympic gold.

Next year, she will be in contention for the Olympic title, after winning bronze in London 2012 — representing Russia despite having lived in Florida since age seven.

“There’s no better feeling than being out on the court having so many people fly here from Russia to support you,” Sharapova beamed on Sunday as the Fed Cup final was under way.

“In an event like this you’re just not playing for yourself, you’re playing for your teammates, for your country.

“It’s a very unique feeling and it’s so special.”

Yet questions over her team spirit continue to follow her.

She has played only five Fed Cup ties since earning professional status in April 2001, two of which were this year.

A decade ago, she was involved in a rift with her teammate and now Russia captain Anastasia Myskina, who threatened to boycott the Fed Cup if Sharapova was selected for the Russian team, complaining about her father’s behaviour in the stands.

Myskina, the 2004 French Open champion, also slammed Sharapova for being “more American than Russian,” accusing her of speaking Russian “with a coarse accent.”

Former fellow Russian player Elena Dementieva once said that Sharapova “grew up in America and trains there, so we don’t have anything in common.”

This week, Myskina waved the spat aside, saying she was happy to have Sharapova on the team.

“Definitely it’s very important to have Maria on the team and I want to say thank you,” Myskina said.

But after the Fed Cup final, she declined to comment on Sharapova’s presence on the team.

“We lost. That’s the end of the story,” she said.

Adding fuel to the fire, Czech media said Sharapova had shunned the rest of the team and stayed in a different Prague hotel to the others.

AFP