Kansas City, MO (SportsNetwork.com) - Reliever Kelvin Herrera, a key part of the Kansas City Royals' surprising run to the 2014 World Series, agreed to a two-year contract with the reigning American League champions on Thursday.

Financial terms were not disclosed, though the Kansas City Star reported the deal, which will cover Herrera's first two arbitration years, will be worth $4.15 million.

Herrera is coming off a breakthrough 2014 campaign as the seventh-inning man in what was the most dominant bullpen in the majors. The hard-throwing right- hander posted a stellar 1.41 ERA over 70 appearances, did not allow a home run in 70 innings pitched, and held opposing hitters to a .214 average.

The 25-year-old also pitched well in the postseason, yielding just three runs and 11 hits over 15 innings spanning 11 games in helping Kansas City to its first AL pennant since 1985.

Over 207 career appearances, all with the Royals, Herrera has compiled a 13-14 record and five saves with a 2.56 ERA.