The Battle of the West shifts north to Mackay on Saturday night in arguably the biggest match in history involving both clubs.
For more than five decades the Eels and Panthers have produced memorable games to claim western Sydney bragging rights but none will have a bigger bearing than this semi-final.
Surprisingly they've only met one time previous to that in the finals - during the first week of the 1985 playoffs.
There have been many players who have lined up for each club over the years including four ex-Panthers in the Parramatta squad - Reagan Campbell-Gillard, Bryce Cartwright, Waqa Blake and Will Smith.
There has also been the likes of former international Michael Jennings, 300-gamer Geoff Gerard, premiership winners Paul Dunn and David Liddiard, as well as the likes of Andrew Leeds, Matt Adamson, Gary Freeman and Frank Pritchard.
NRL.com takes a look back at some of the best Battle of the West matches involving the clubs.
Panthers v Eels - Semi-Final
Penrith v Parramatta – Top 10
Round 16, 1968 - Little brother beats big brother
Parramatta pummelled the Panthers when they first entered the competition in 1967 and after another loss against a more experienced Eels line-up in round five, Penrith announced themselves to their arch-rivals.
Penrith Park played host to the upset with the Panthers securing a 14-12 win in front of their faithful courtesy of a double to Bob Mara.
The result pushed the Eels out of finals contention after they were fifth going into the clash.
Minor preliminary final, 1985 – Panthers run into Eels brick wall
The Tim Sheens-coached Panthers qualified for their first finals campaign after edging out Manly 10-7 in a mid-week playoff for fifth spot.
They backed four days later against the Eels at the Sydney Cricket Ground in the semi-final, but were no match for their rivals, going down 38-6.
Rampaging winger Eric Grothe scored two of Parramatta’s seven tries.
1986 - Panthers defy odds and cause upset
The Panthers made amends for their semi-final defeat a year earlier with a hard-fought 16-12 defeat of eventual premiers Parramatta in an absorbing contest in Penrith.
Panthers prop Paul Akkary was sent off for a high tackle eight minutes into the clash but the home side defended their way to victory against an all-star Eels outfit.
Club legend Greg Alexander was playing a rage game at five-eighth with Greg Clements lining up at halfback.
Penrith's ability to defy all odds to win the game brought two standing ovations from the supporters at half-time and when the siren sounded.
Semi-final, 2000 - Rivarly shifts east for sudden death clash
The neutral Sydney Football Stadium in the city's east played host to both western Sydney clubs in the 2000 semi-final with 25,746 making their way to the ground.
Penrith was on track to lock in a finals appearance early in the year but suffered a major mid-year slump before winning 10 of their last 13 games to finish fifth.
Parramatta locked in seventh spot but the gap between them and the Panthers was only one competition point apart.
The Eels had struggled more than Penrith to score points in the 2000 season but were able to pile on four tries against their counterparts to win the second finals game between the two sides 28-10.
The result ended the year for the Panthers, who bowed out in straight sets.
Round 17, 2009 – Jennings sparks dream debut for Panther
A sunny afternoon in Sydney's west brought about plenty of points in the 2009 clash in Penrith as both sides were looking to stay within reach of the top eight.
The Panthers were debuting young winger Junior Tia-Kilifi on the left edge but it was his centre partner Michael Jennings who proved the difference to set up the debutant for the match-winning try with two minutes left on the clock.
Parramatta regained possession at the restart to give themselves a last-minute chance to bounce back but Fuifui Moimoi's offload went astray in the see-sawing contest.
Round 19, 2010 - Hayne magic seals comeback
A packed and vocal crowd of over 22,000 descended to Penrith for the only Battle of the West clash of the season with the Panthers putting on a show early for a 22-0 lead.
After a barnstorming finish to the 2009 season, Jarryd Hayne's influence on the Eels outfit wasn't as dominant in 2010 but was enough to spark the side into a remarkable comeback.
The Eels racked up 30 unanswered points to snatch the lead before Wade Graham narrowed the lead late.
Penrith had one last roll of the dice on the siren but couldn't come up with the miracle play to hand the Eels a remarkable win.
Round 19, 2011 – Panthers spoil Hindy's party
Another classic finish between both clubs with a try on the siren to Panthers five-eighth Travis Burns sending the game into golden point with scores locked at 22-22 after 80 minutes.
The Eels looked like escaping with the win but Luke Burt's first field goal attempt hit the uprights in extra time before Panthers halfback Luke Walsh stepped up a minutes later to slot the winner.
The result was agonising for Eels club legend Nathan Hindmarsh who notched his 300th game in blue and gold.
Round 16, 2012 - Sandow nails match-winner
Desperation was high between the two clubs in 2012 with Parramatta languishing at the bottom of the ladder after 15 rounds and Penrith just above them in a dark year for both clubs.
Few outsiders would've been able to tell that was the case in round 16, however, when over 15,000 diehards descended a Penrith to try and get their side over the line.
The Panthers looked on track for victory when they enjoyed an 18-6 lead midway through the second half but Parramatta stormed home with tries to Jarryd Hayne and Luke Burt to send the match into golden point.
Some second phase from Joseph Paulo and Nathan Hindmarsh got the Eels up-field with a minute left in extra time before Chris Sandow slotted a field goal to secure their third win of the year.
2016 – Round 5 – Cartwright wins it on the bell
The Panthers welcomed Matt Moylan back from a long injury lay-off and were hoping he'd be the man to spark their early-season slump in the latest edition of the local derby.
However, it was another local junior, Bryce Cartwright, who starred for the Panthers with the back-rower crossing for a double - including the 78th-minute match-winner - after the Panthers ran down an 18-12 deficit in the final five minutes.
Josh Mansour's try in the 75th minute wasn't converted by Jamie Soward but the Panthers five-eighth provided the kick late for Cartwright to cross on the buzzer.
2016 - Round 19 – Penrith add to Eels' woes
Both sides met again following their round five thriller but in far different circumstances more than three months on.
The Panthers were looking to keep their finals hopes alive after slumping to 10th while the Eels had been stripped 12 competition points in May following salary cap breaches.
Parramatta took an 18-6 lead into half-time but were run down by their rivals in the second half with three tries.
Despite the Eels' best efforts late, the Panthers hung on to pile on more pain and secure another gripping win.