They failed to score a point in the second half as Rob Elloway, Matt Evans and Joe Atkinson were yellow-carded.
"The communication was there, we just weren't reacting to what he (the referee) was saying," Davies said.
"The cumulation caught up with us with three yellow cards - you don't often see that, but they were justified."
Pirates had beaten their Championship rivals in all three of their previous meetings this season.
Evans and on-loan Exeter scrum-half Stu Townsend scored tries for the Cornish side, who will lose head coach Davies in the summer due to budget constraints.
"In that first half that's all that was keeping them in the game, our ill-discipline," he told BBC Radio Cornwall.
"Ill-discipline came back to haunt us - it was one bridge too far.
"There have been some dark days and some long days, so to get to a final would've been great, but we haven't achieved that."

Christopher Clarke, 29, contacted girls, aged 15 and 16 at the time, via Facebook, Snapchat and Twitter.
He also bought the Ysgol Bro Dinefwr pupils gifts including T-shirts, earrings, sweets and games consoles.
An Education Workforce Council hearing concluded his actions amounted to professional misconduct.
One girl told how Mr Clarke sent her a message saying: "I kept having the same thought over and over again. How much I wanted to grab you, kiss you..."
The girl, now 19, said he also invited her to one-on-one sessions in his chemistry office and told her not to show anyone the gifts her gave her.
Another girl, now 17, said his actions made her feel uncomfortable and he was "acting in a creepy nature".
A third student said she told Mr Clarke she thought his messages were inappropriate and he later asked her to delete their conversation.
Police investigated but no charges were brought against Mr Clarke.
The school also began an investigation but he resigned before any findings were made.
Education Workforce Council chairman, Steve Powell, said Mr Clarke's conduct "clearly breached boundaries between teachers and pupils".
"His actions fell very short of the standards expected of a registered person and amounted to unacceptable professional conduct," he added.

The body of Peter Wrighton, 83, was found three miles south of East Harling in Norfolk on 5 August. He had been repeatedly stabbed.
Norfolk Police said they wanted to trace three men seen around the woodland close to the time he died.
The force said a man in his 50s seen changing into a t-shirt has been found.
Police say they still want to speak to two other men; one aged 25 to 30, with tanned skin, wearing a grey or blue t-shirt, grey gym shorts and heavy-duty flip flops; the other aged 30 to 50, wearing dark clothing and seen walking without a dog to the north of the heath.
Det Supt Andy Smith added: "We have already heard from more than 220 people but we will be exploring all avenues in our enquiries and we are still keen to hear from more.
"We also want to hear from delivery drivers who might have travelled through or have been in the area on Saturday and who could have important dash cam footage for us to review. In addition, anyone else with images or footages of the area should contact us."
There have been no arrests and no weapon has been found.
Mr Wrighton was pictured on CCTV using the post office in Kenninghall at 10:10 BST, about 35 minutes before his body was found near to Fiveways Junction.
"His car, a red Skoda Fabia, was parked close to The Street, the road close to the heath land where he was walking his dogs Dylan and Gemma," Det Supt Smith said.
The force said it has more than 100 officers and staff working on the "significant murder investigation".
Cornish Pirates boss Ian Davies says ill-discipline "came back to haunt" his side in their 36-15 British and Irish Cup semi-final defeat at London Welsh.
[NEXT_CONCEPT]
A Carmarthenshire teacher who sent thousands of sexual messages to three pupils has been banned from teaching for five years.
[NEXT_CONCEPT]
One of three "vital" potential witnesses to the murder of an elderly dog walker in woodland has been traced, police have said.