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What you need to know this week: The NL's hottest ace, MLB's ERA leader on the trade block

Zack Greinke is back to dealing like an ace, which makes his Thursday showdown against Pittsburgh's Gerrit Cole a matchup you won't want to miss. Norm Hall/Getty Images

This week's action puts a new group of stars in the spotlight, from Arizona's ace delivering, to an Astro who might be ready to lift off when Houston heads to New York later this week. Who is the hitter or pitcher you need to follow? What's the rumor you need to know about for its impact on your team's postseason hopes? Who is the fantasy asset you want to have in your lineup? And who is the Ranger whose slow rehab from injury you need to keep tabs on?

The pitcher whose start you should catch: Zack Greinke, Arizona Diamondbacks. There are four starting rotations currently averaging more than a strikeout per inning: the Red Sox, Indians, Dodgers and Greinke's Diamondbacks, whose 9.55 whiffs per nine innings lead the National League.

One key to the D-backs' whiff-happy staff has been Greinke's turnaround. After struggling during his Arizona debut a season ago, Greinke has reverted to his Cy Young form and will enter his next start on a roll. Over his past four outings, Greinke has struck out 33 while walking just three batters.

If this week's pitching probables hold up, Greinke will face another hot starter in Pittsburgh's Gerrit Cole on Thursday. Cole has 31 K's against five walks in his last four starts, so it should be a matchup to watch. -- Bradford Doolittle