Of all the concerns about the Rangers, among them their inability to find the defensive lockdown game that identified the club last season, the most disturbing is the diminished play of Brad Richards, who had such a difficult time last night he was benched for all but one shift in the third period of the Blueshirts’ 4-3 shootout loss at the Garden to the Islanders. Richards, who got a pair of shifts in overtime, could not get out of his own way, let alone elude opponents. Moving the puck not only became impossible, so did holding on to it through an unsettling series of shifts in a second period during which the Islanders scored three times in a span of 6:56 to take a 3-2 lead before Carl Hagelin knotted it midway through the period. “It’s on me,” said a somber Richards, who did show speed in the first in going to the net for a shot and then his own rebound that Marian Gaborik converted for a 2-0 lead at 11:28. “I couldn’t make a play in the second; there’s really not much else [to say].” The bottom fell out on Richards during a stretch early in the second period when the Rangers had a power play of 3:27 that included 33 seconds of five-on-three. That’s when Richards repeatedly turned over the puck, allowing the Islanders to seize momentum. “I was trying too hard there,” said Richards, who has four points (0-4) the last eight games. “I wanted to move the puck, I was trying too hard and that’s why I got into jams. “I’m smarter than that.” Coach John Tortorella, who elevated Brian Boyle into Richards’ spot between Gaborik and Ryan Callahan, answered in the affirmative when asked if benching the 32-year-old pivot was “a drastic step.” “It’s a pretty big hole to fill but I felt I had to,” said Tortorella. “He was struggling. [But] it’s not at all for lack of effort.”