Edinburgh scrum-half Greig Laidlaw was critical of French referee Jerome Garces after the capital side's 23-14 defeat by Glasgow Warriors.
Glasgow not only took the Pro12 league points but also established a nine-point lead in the 1872 Cup.
"I was disappointed at the referee, the way he allowed them to run the blockers on the line," said Laidlaw.
"I spoke to him before the game about that and he let three of them go in the first half."
The Scotland international thought his side were capable of overturning the scoreline and winning the Cup on aggregate after next Saturday's second leg at Murrayfield.
"We've got to repeat our second-half performance," Laidlaw told BBC Scotland. "If we play like that, we'll not be far away.
"But, credit to Glasgow, they stuck in and scored a few nice tries in the first half."
DTH van der Merwe crossed the line twice, with Rob Harley adding Glasgow's third try, before Laidlaw's boot and a Piers Francis try reduced the arrears.
"That's the most disappointing thing, the first half," said Laidlaw. "That's what cost us the game.
"We just got on the front foot a little bit. We stopped their blockers running into our defensive line.
"I was disappointed at how we dealt with that in the first half."