David Montgomery, 39, was giving evidence for a third day in the trial of 48-year-old Ronnie Coulter.
When Mr Findlay accused him of being "a persistent liar" over his differing versions of events, the witness called the QC a liar before being ordered to apologise by judge Lord Matthews.
Mr Coulter denies murder and has blamed Mr Montgomery and another man.
Mr Coulter, from Wishaw, is accused of murdering Mr Chhokar in Garrion Street, Overtown, North Lanarkshire, on 4 November 1998 by stabbing him.
He has lodged a special defence blaming his nephew Andrew Coulter and Mr Montgomery.
On Monday, as the trial entered its third week, Mr Montgomery was taken through his various versions of events.
The jury at the High Court in Edinburgh had previously heard that Mr Coulter, his nephew and Mr Montgomery had approached Mr Chhokar on the night he died amid a row about a stolen Â£100 Giro cheque.
Mr Montgomery said that Ronnie Coulter said: "Andrew - just hit him."
The jurors heard that the first time Mr Montgomery mentioned this was in a statement given to police on 18 December 2014.
He did not mention it in his first statement to police, given three days after Mr Chhokar's death.
He also did not mention it at his own trial for the murder of Mr Chhokar in 2000 - a charge of which he was cleared.
At his trial, he claimed that the only words spoken were by Andrew Coulter who asked Mr Chhokar who had cashed the Giro.
During his cross-examination on Monday, Mr Findlay said to Mr Montgomery: "You are lying when you said Ronnie said 'Just hit him,'" and he replied: "I'm not lying."
Mr Montgomery was taken through his versions of events which were given to the police and in court and Mr Findlay then said: "You are, if not an accomplished liar, a persistent liar."
The witness responded by saying to Mr Findlay: "You are a liar."
Mr Montgomery was then asked to repeat what he had said and trial judge Lord Matthews asked: "Why are you accusing counsel of lying."
The witness then said: "Because he is making things up."
Lord Matthews told Mr Montgomery: "Counsel is not making things up," and ordered him to apologise to Mr Findlay. The witness then said: "I'm sorry I'll apologise."
In previous evidence to the trial, Mr Montgomery also told the jury that he saw Ronnie Coulter appear to punch Mr Chhokar.
Mr Findlay said: "When you were asked about this you said: "I think it was one hand, I honestly don't know. You are trying to help Andrew Coulter by making out Ronnie was punching with one hand. You want people to think that was Ronnie stabbing him," and Mr Montgomery replied: "I'm trying to recall as best I can."
Mr Montgomery was shown a transcript of his trial in which he said that he saw Ronnie Coulter punching with both hands.
Mr Findlay then said: "People fighting use two hands and people stabbing use one hand," and Mr Montgomery replied: "Yes."
The QC added: "In this trial you are trying to suggest it is more consistent with an attack than a fight," and Mr Montgomery said: "That's how I recall it."
Mr Findlay added: "The background is the family decided Andrew had done it, but because he was only 17 Ronnie should take the blame for it," and Mr Montgomery replied: "I don't know where you've got that from."
The QC said: "When the ladies and gentlemen of the jury have to assess your evidence they may want to bear in mind when you are facing incontrovertible evidence, you are quite happy to lie to the bitter end," and Mr Montgomery replied: "Yes."
Mr Montgomery was asked why he made up a story just three days after Mr Chhokar's death, telling police he had been in Overtown that night to buy counterfeit cigarettes from a man called Kevin, instead of admitting he had been there when he died.
He said he was scared and added: "I just remember fear."
The witness later denied that he saw Andrew Coulter murdering Mr Chhokar.
Mr Findlay said to Mr Montgomery: "You and Andrew Coulter were the last two people to be near to Chhokar before he died," and he replied: "Yes, me and Andrew."
Mr Montgomery was then told by defence QC Donald Findlay: "What happened that night after Ronnie had gone was that Andrew lost it and pulled out a knife and stabbed Chhokar and murdered him," and the witness replied: "No."
Mr Findlay added: "You could come to only one conclusion that Andrew Coulter had murdered Coulter," and Mr Montgomery replied: "No that was the wrong conclusion. He never killed him."
The trial before judge Lord Matthews continues.
A witness in the Surjit Singh Chhokar murder trial has apologised for calling defence QC Donald Findlay a "liar".