Kinsler was unable to field Yonder Alonso's two-out grounder cleanly, allowing the tying run to score. Later in the inning, two more scored on Billy Butler's pinch-hit bloop single, which landed just in front of center fielder Cameron Maybin.
All three runs were unearned and cost starter Mike Pelfrey a shot at getting his first win of the season.
"Baseball's a weird game. You can't lose focus at any moment," Kinsler said. "You lose focus, and things like that happen. The tough part about it is [that] Pelfrey has been pitching well, and we're trying to get him over that hump. To not come up with that play, it hurts a little bit."
Kinsler, a four-time All-Star, is widely considered to be one of the best defensive players in the game. He has made only three errors this season -- all of them this month -- after playing error-free for Detroit's first 35 games.
He was in position to field Alonso's grounder, too, but couldn't come up with the ball. He might have been distracted by Oakland's Khris Davis, who was running from first to second, but he wasn't making excuses.
"We just had a couple of bad breaks," he said. "I should have come up with that ball. Cam missed the ball in center field by a couple inches, and that's the game. We understand that we need to win close games, and that's why it hurts today, but you have to turn the page. You can't sit here and dwell on it."
Pelfrey, who took the hard-luck loss and fell to 0-5, defended Kinsler, as did manager Brad Ausmus.
"Ian's the best second baseman in the American League," Ausmus said. "It's obviously unfortunate timing. Big picture, he's the best in the league. I'll take a ball hit to Kinsler any time."
Pelfrey was just as forgiving.
"In my mind I think he's probably the best second baseman in the game, and that's a play he makes every day," Pelfrey said. "Obviously that stuff happens but he brings it every day. It's unfortunate that that had to happen."