Great Britain set up a winner-takes-all Fed Cup clash with Hungary but their victory against Greece was dogged by controversial line calls.
Britain made it two from two to sit top of Pool A of the Europe/Africa Zone Group 1 going into the final round-robin tie after Katie Boulter and Johanna Konta won their singles matches.
But there were questionable line calls throughout and Konta's opponent Maria Sakkari condemned the line judges as "the worst I have ever seen in my life".
Boulter's opponent Valentini Grammatikopoulou also suggested the home judges were not playing fair as the matter cast a shadow over what was a thrilling tie.
Boulter delivered another opening win as she battled hard to triumph 6-3 4-6 6-3 before Konta made sure the tie was in the bag after coming from a set down to beat Sakkari 4-6 6-2 6-3.
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Both sides were on the end of calls that looked wrong, but with no Hawkeye in operation the players had no choice but to accept the decision.
Afterwards Sakkari, who is ranked one place higher than Konta at 38, did not hold back in her assessment of the officiating.
"They are terrible," she said. "Since the first round. They're the worst I've ever seen in my life.
"This is unacceptable. Because we have many players in the top 100, we are playing with poor balls, 9 and 11 change, and with line umpires that have never worked in their life. That's what I want to say.
"The chair umpires are great, but the line umpires are the worst I have ever seen in my life.
"We are used to playing with very good professionals and we come here, it's a very high level Fed Cup tie, we need to have good professionals on our court."
With Hungary beating Slovenia to also make it two from two, whoever wins the best-of-three tie will advance to play the winner of Pool B - either Croatia or Serbia.
GB captain Anne Keothavong, whose brother James is an ATP Tour umpire, insisted the disputed calls, which all seemed to come at crucial moments, had no impact on the outcome of the matches.
"I have to be diplomatic as I can," Keothavong said. "The line calling today didn't affect the outcome of the matches."
