Both teams were hoping to finish disappointing campaigns positively on Sunday but it was Bulgaria who triumphed with a 3-2 (19-25, 25-22, 25-18, 22-25, 15-12) win to finish the VNL with a 6-9 record.
Penchev and Bratoev were brilliant throughout with 21 points apiece but were almost matched by Sung-Min Moon (15 points) and Jae-Duck Seo, who changed the course of the match with a brilliant backend to finish with 15 points.
The result means Korea won just once in the tournament to finish last on the overall standings and they will now play a relegation match against the winners of the Challenger Cup to remain in the VNL.
They were made to work for the victory but it ensured Bulgaria stretched out their dominance at the major world level over Korea to 16 matches since 1994.
With only pride on the line, Bulgaria made a fast start with a Georgi Seganov ace but he followed with a service error as the early going was marked by mistakes in an uninspiring opening. Making a mockery of their lowly overall standing, Korea looked the goods through the aerial prowess of Jung Jiseok as the teams traded points through service struggles.
Bulgaria attempted to blast their way back into form highlighted by several booming blows from Nikolay Uchikov but their bane on serve continued to gift away points. Astoundingly, Bulgaria went a large part of the set without winning a point on serve and Korea - sensing a rare set triumph - made them pay. Moon spectacularly finished well-crafted sets in a commanding performance to lead Korea's decisive opening set charge.
After their first set letdown, Bulgaria aimed to shake from their stupor and a leaping Penchev did his best to energise his lethargic team.
Not only providing the pyrotechnics, Penchev also inspired through tenacious defence but Bulgaria's renewed resiliency was being thwarted by Moon's dominance at the net as Korea could sense an opportunity to claim just their second victory of the VNL. Svetoslav Gotsev, the leading stuff blocker in the VNL, was standing tall to defiantly stymie Korea's momentum and Bulgaria was finally winning points on serve.
In a reversal of the first set, Korea suddenly had the wobbles on serve and Bulgaria seized the opening through some heavy-hitting from Bratoev to level the match.
Bratoev continued to stamp his class on the contest as the shift in momentum was evident with Bulgaria's firepower starting to overwhelm Korea despite the best efforts of libero Minsu Jeong who produced several outstanding hustling efforts.
The Europeans dictated the rallies and muscled a slumping Korea around the court to wrap up a comprehensive third set.
Determined not to let slip a 2-1 advantage like they infamously did against Germany on Friday, Bulgaria were keen to wrap things up but superb blocking from Seo, who provided a spark off the bench, helped engineer four straight points for Korea who reached the first technical timeout with an 8-6 lead.
Bulgaria steadied through strong serving from Penchev but the southpaw Seo was proving the difference in the stanza with scintillating all-round play. A joyful Korea were playing with spirit and boundless energy to ensure the set went down to the wire.
At 19 apiece, a costly serve into the net from Penchev triggered Bulgaria's downfall as Seo - who scored nine points for the stanza - continued his purple patch to ensure a fifth set decider.
A red-hot Seo made his mark immediately in the fifth set with unwavering accuracy but Bratoev answered as Bulgaria reeled off six straight points to skip out to a 6-2 lead. Bratoev seemed set to seal the deal with a deft put away giving Bulgaria a handy 11-7 lead but Korea fought back to get within striking distance.
However, fittingly, Bulgaria finally closed it out through a Bratoev thunderbolt to ensure they finished the VNL with gusto.