SAN FRANCISCO -- Even as his Giants are battling to advance to the World Series, general manager Brian Sabean looks around and sees his NL West rivals already gunning for San Francisco next year.

You bet he took note when the Diamondbacks slithered into action Saturday by acquiring reliever Heath Bell from Miami and shortstop Cliff Pennington from Oakland.

"That's the nature of our division," Sabean said Sunday afternoon as the Giants prepared for Game 6 of the NLCS. "Our division is very competitive and very underrated.

"I say it every year. Every year, it's a shotgun start in our division. And it will be the same next year."

With Bell, if Arizona can get him back on track, the Diamondbacks could have a lockdown bullpen next season. General manager Kevin Towers says he envisions Bell as his seventh-inning guy, David Hernandez for the eighth and J.J. Putz to close. Plus, ground-ball specialist Brad Ziegler will be an important factor.

"I can see why they did it," Sabean said. "A strong bullpen is very important. A lot of tight games are played in this division."

Historically, Towers has had great success in building potent bullpens, both in San Diego and in Arizona. In fact, in Towers' two seasons with the Diamondbacks, the franchise has a major league-best improvement of knocking 2.50 off the bullpen's ERA. In 2010, the Diamondbacks pen posted one of the worst bullpen ERAs in modern times at 5.74. In 2012, the Diamondbacks posted a franchise-best 3.24 bullpen ERA.

"That's been his history in San Diego," Sabean said.

The Hot Stove League season hasn't even formally started yet, and already things are moving in the NL West.

"It seems like somebody gets off to a fast start every year in our division, and it's almost contrary to who's favored," Sabean said.