Derek Lowe's strikeout rate stands at 8.3 K per 9 innings this season against a career rate of 5.9 K per 9 IP. That represents a huge increase for an older pitcher, and especially one that depended on a great sinker and ground ball outs for most of his career. His slider stands as his best strikeout pitch, as 33% of plate appearances that end with a slider see the batter going down on strikes.
Lowe gets great movement on the slider, breaking down and toward the catcher's right hand:
Lowe uses this movement effectively. If he starts the pitch over the plate, it ends up on just off the plate low near the catchers hand. This is where he gets the swinging strikes:
If Lowe starts the slider off the plate to the catcher's glove hand, it comes back in and catches the corner of the strike zone. This is where he catches batters looking.
One change that might have enhanced the effectiveness of the slider was Lowe's addition of a cut fastball. The cutter and slight show the same deflection in the horizontal plane, the slider break down more. Lowe also tends to throw the cutter over the plate. The two pitches may look enough alike that batters start to swing at what they believe is a cutter over the plate, then get the slider in. For some who maxes out at about 86 MPH, that's impressive use of his arsenal to post a high K rate.