The Giants owe much of their success to the relievers known as the "Core Four" -- Jeremy Affeldt, Santiago Casilla, Javier Lopez and Sergio Romo. In an era when economics or fluctuations in performance force many teams to replenish or revise their bullpen personnel almost annually, the Giants' stability and excellence are truly singular.
History proves that.
Affeldt, Casilla, Lopez and Romo each has exceeded 35 appearances for four consecutive seasons. According to MLB.com research, no ballclub since at least 1980 has possessed a quartet with equal durability for that long a period.
"When you have the continuity and consistency that we've had, it's a luxury," Lopez said.
The Giants have basked in this luxury. During the aforementioned four-year span, the "Core Four" recorded an aggregate 2.45 ERA in 1,005 appearances. Their opponents' batting averages almost disappeared in this stretch (Romo .199, Casilla .203, Affeldt .226 and Lopez .229). They excelled even more during San Francisco's postseason trips in 2010, 2012 and 2014, combining for a 1.14 ERA.
"It's all about slowing down the heartbeats when you get in those pressure spots," Lopez said. "I feel like that's one thing that we're really good at."
The quartet's effectiveness bolsters manager Bruce Bochy's reputation for adept bullpen maintenance.
Said Affeldt, "I think he understands that he needs to give guys breaks when they need breaks, but he also makes sure they're in there consistently. Bullpen guys, if we don't have consistent appearances, we're not very good."
Each pitcher's style is distinct from the others, a variety that benefits the Giants. Affeldt and Lopez are both left-handers, but the former throws an array of stuff from a basically traditional motion while the latter relies on off-speed deliveries and deception while employing essentially a sidearmed release. The same goes for the right-handers: Romo barely exceeds 90 mph with his fastball, but his slider remains formidable. Casilla isn't as precise as Romo but throws harder.
"We don't do anything alike," said Romo, who has twice exchanged the closer's role with Casilla and is currently the Giants' top setup man.
Bullpens featuring multiple relievers whose fastballs approach or exceed triple-digit velocities have become fashionable. The Giants faced one of these crews in last year's World Series, as Kansas City challenged them with Kelvin Herrera, Wade Davis and Greg Holland. But the Giants' bullpen sparkled in the postseason while recording a 2.11 ERA.
"They're the 'sexy' bullpen," Affeldt said of the Royals. "They had the 100 mph fastballs coming every five seconds at you. We got the same outs; we just did it a little differently."
"Velocity gives you more window for [error]," Lopez said. "But I do think we are showcasing the fact that you can have a 'pitchable' bullpen."
Besides, an intriguing change comes over the "Core Four" during postseasons. They have proven they can get a strikeout when one is necessary, amassing 70 in 78 2/3 innings during the Giants' last three postseasons.
The quartet's vast experience with each other has deepened their insight. For instance, they immediately realize when one of them is struggling on the mound.
"I know how to read the game or read my teammates to see if something's wrong or they need some help," Romo said.
These guys rarely remain a foursome after the game ends. It's not necessary.
"Although we may not be the best of friends off the field, we're very close in this clubhouse, we're very close in the bullpen and we're very close when we compete throughout the season," Romo said.
They and the Giants share a mutual satisfaction. Affeldt, Lopez and Romo each spurned opportunities to depart as free agents. Casilla relinquished two cracks at free agency by signing a three-year, $15 million contract before the 2013 season.
"I think that just shows you how we feel about the team, the front office, how things are," Affeldt said.
Romo was widely assumed to be headed elsewhere until he signed a two-year, $15 million pact in December.
"Romo's coming back is a big deal," Lopez said. "It really is."
Romo didn't want to be the one to break up the group.
"Those three guys were a big reason why I wanted to stay," he said. "They're good men. They're very reliable and consistent. It's very easy to respect and appreciate those men."
Chris Haft is a reporter for MLB.com. Read his blog, Haft-Baked Ideas, and follow him on Twitter at @sfgiantsbeat. This story was not subject to the approval of Major League Baseball or its clubs.