By Bruce Levine–

CHICAGO (CBS) — The rivalry between the the division rival Cubs and Pirates has heated up significantly since the start of the 2015 season, but it’s been lopsided this year. two division rivals has heated up significantly over the past year and a quarter On Friday afternoon at Wrigley Field, right-hander Jason Hammel and his Cubs dominated the Pirates in a 9-4 win, their fourth win against Pittsburgh in as many games this season.

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Hammel allowed one earned run in 6 2/3 innings, continuing his excellence in moving to 5-0. He now sports a 1.77 ERA. Chicago moved to 26-8 and now has a 7.5-game lead on second-place St. Louis entering play in the evening. Pittsburgh is eight games back.

“It’s the Pirates-Cubs rivalry,” Hammel said after another intense game. “I would not expect anything less. This is a great atmosphere here at Wrigley all of the time. Anytime you get enemy colors here from the same division, you know it’s going to be a pretty heated game, probably a well-played one as well.”

The Pirates lost infielder Jung Ho Kang in a takeout slide by former Cub Chris Coghlan last September, which really amped up the mutual dislike between the clubs. That intensity increased significantly after Cubs ace Jake Arrieta then shut out the Pirates in the high-stakes wild-card game in the playoffs.

Last week in Pittsburgh, the Cubs beat the Pirates by scores of 7-2, 7-1 and 6-2. Friday’s carnage included a three-run home run from Addison Russell, a three-run blast by David Ross and a solo shot from Kris Bryant.

The teams have 14 games left against each other, so the bad blood will likely continue.

“It’s a great thing,” Cubs president of baseball operations Theo Epstein said about the ferocity between the teams. “Baseball is at its best when you have good rivalries with teams that maybe don’t like each other but respect each other. These games have been pretty intense and pretty entertaining. The reason these games mean something is Pittsburgh has turned itself into an outstanding, winning franchise. What they have done the last three years or so has been pretty amazing. We know the Pirates and Cardinals are not going (away). We will have to play really, really well in 162 games to beat them.”

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The run differential has been humiliating thus far for the Pirates, as the Cubs have outscored them 29-9 this season.

Can a team get into another club’ collective head?

“From experience, I have been on the other side of that and it can bother you some,” Cubs manager Joe Maddon said.

“They have such a wonderful team and many great professionals on that team. So I don’t think that is the case with them. They are really good. I doubt it. To this point, we have had a nice little run. I don’t take anything for granted.”

The Cubs just know they won’t be giving the Pirates bulletin board material.

“The more teams beat me and my team, the more I wanted to beat them worse,” veteran catcher David Ross said. “I don’t know if you get into their heads or whatever. You kind of have to go out there play. It is all about execution. They are a very talented team. It is a battle every time we play them. We expect that to continue.”

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Bruce Levine covers the Cubs and White Sox for 670 The Score and CBSChicago.com. Follow him on Twitter @MLBBruceLevine.