Johnny Sexton and Ronan O'Gara are "ferocious competitors" whose one-time rivalry on the pitch pushed Sexton to surpass the records set by his predecessor as Irish fly-half, former Ireland fullback Hugo MacNeill told AFP.
Sexton, 38, dethroned O'Gara as Ireland's record points scorer on Saturday as his 16 points in a World Cup pool game against Tonga took him to 1,090 points, seven more than O'Gara achieved.
The record came a week after Sexton passed the retired Munster legend's Rugby World Cup points record for Ireland.
Saturday's milestone is the third record Sexton has prised from O'Gara's grasp this year, having become the all-time Six Nations points scorer when he captained Ireland to the Grand Slam-sealing win over England.
Records, though, are just one part of the story.
Sexton may have two Grand Slams, in 2018 and this year, to his credit but it was O'Gara's nerveless drop goal in 2009 to beat Wales in Cardiff that ended Ireland's 61-year Grand Slam drought.
"They are both ferocious competitors, no more so than when they faced each other playing for Munster and Leinster," said MacNeill.
"The Munster-Leinster rivalry was fantastic for Irish rugby.
"Johnny Sexton was more frustrated than anyone watching Munster, thanks to the orchestration of O'Gara, dominate for so many years.
"It resulted in Sexton being the driving force that propelled Leinster to the summit.
"It was a great dynamic to have both of them spurring each other on, there was a great rivalry and great respect between the two of them."
Sexton's competitiveness made an impression on O'Gara's Munster teammate Marcus Horan on Ireland's tour of New Zealand in 2010.
Sexton lost a game of pool to Horan and everyone dispersed, or so the others thought.
"I recall walking back into the team room having gone away for a few hours and finding him (Sexton) there having not moved all day as he was waiting to challenge me to another game," Horan told AFP.
"That shows you his determination to win, no matter what it was."
- 'Leave a legacy' -
MacNeill said in terms of style of play there is little to choose between the two, quoting "an old Welsh description of fly-halves".
"They are either high church, disciplined, controlled and with a structured game, or chapel, more populist and crowd pleasing.
"I would say both O'Gara and Sexton are high church."
Tony Ward, regarded by many as Ireland's most individually gifted fly-half although he told AFP you cannot compare the professional era with the amateur one, says both Sexton and O'Gara possessed the essential ingredient to be a great fly-half.
"The one thing you want to see in a 10 is blindingly obvious," said Ward.
"It is the same with an NFL quarterback, you need presence in those positions and both of them have that in abundance.
"When on the field they are, or were in O'Gara's case, in control."
MacNeill, 65, says nothing should be read into Sexton being captain, since the 2019 World Cup, and O'Gara never having that honour.
"Sexton obviously is a great leader but Ronan is a very good leader too," said the 37-times capped MacNeill, a member of two Triple Crown-winning sides.
"O'Gara very much acted as a leader, especially in 2009 when he dropped the goal two minutes from time with the Irish 15-14 down.
"That was his leadership."
Ward is not so laudatory about Sexton as a captain, saying the tongue lashings he gives teammates can have a negative impact.
"I urge him to try and remain positive, as he is at the moment, for when he is negative and giving out to others it is not what a team needs," said the 68-year-old.
"Not everybody has the same personality as him."
Ward, though, says that as Sexton joins O'Gara in retirement at the end of the World Cup campaign his absence will only underline the immense impact that both had on Irish rugby.
"I would answer unequivocally they leave a legacy," said Ward.
"In terms of how they played -- not always the way they acted -- encouraging young kids to be the next Ronan O'Gara or Johnny Sexton.
"They have had a huge influence on the further development of the game in the country."