But manager Jeff Banister wasn't at all bothered by the error, since the Rangers have won two straight games with an opposing left-hander on the mound and Napoli in left.
So Banister is planning to have Napoli back out there on Wednesday night, when the Rangers face Astros left-hander Dallas Keuchel. Joey Gallo started in left on Tuesday with right-hander Collin McHugh pitching for the Astros.
"I don't consider it an experiment," Banister said. "With Mike Napoli playing in the outfield, the reward is on the offensive side. We are going to continue to have Mike work and be out there. My guess is the more he plays, the more confident he'll be."
Over his 10-year career, Napoli was a catcher and then a first baseman. He never played left field until Sunday. The only ball that's been hit to him is the fly ball off the bat of Jose Altuve in the fifth inning on Monday.
Napoli dropped the ball in the swirling wind, but he was not the only fielder to have trouble on Monday. Astros third baseman Jed Lowrie dropped Prince Fielder's high pop in the first inning, and Fielder ended up scoring. Altuve did not.
"I know we want the best defense out there, but we haven't mounted a real challenge to left-handers," Banister said. "We have beaten left-handers, but in our complete body of work, we have struggled against left-handers. With all the other guys that have been out there, we haven't been getting the offense. The ball found him, we didn't make a play. We'll keep working at it."
Odor improving defensively: Rougned Odor went into Tuesday's game having made three errors in his last five games. That left him with a .966 fielding percentage, the lowest among American League second basemen.
On the flip side, Odor has a range factor of 4.95 chances per nine innings, the highest in the league. So he is making plays, and there have been some good ones, including a double play in the ninth inning on Monday. He also made a terrific catch on a force play in the fifth on a throw from third baseman Adrian Beltre that skipped in the dirt.
"I have been working on my defense," Odor said. "I know I make errors, but I still feel good on my fielding. Right now I am not thinking about me, I'm just doing the best I can to win the game."
Offensively, Odor has an .801 OPS, second highest among second basemen in the AL. He trails Jason Kipnis (.843) but is ahead of Altuve (.795), Ian Kinsler (.790), Dustin Pedroia (.783), Robinson Cano (.774) and Brian Dozier (.774), among others.
That is after the slow start to his season, which led to a demotion to Triple-A Round Rock on May 11. He is hitting .313 with 12 home runs and 43 RBIs in 72 games since being recalled on June 15, but the Rangers sent him to Round Rock to work on his defense as well as his offense.
"I think he is settling in and allowing his natural ability to play, that's the best way I can describe it," Banister said. "There have been measurable increases in improvement, but he still has a ways to go. I like the fact that he is in the right place and focused on every pitch. He is not afraid to make a play."
• Fielder's two-run home run in the eighth inning on Monday gave the Rangers a two-run lead and was his 18th career go-ahead home run in the eighth inning or later. That's the third most in the Major Leagues since 2005. Albert Pujols and Adam Dunn both had 19.
• Catcher Robinson Chirinos, sidelined with a torn tendon in his left shoulder, did some throwing on Tuesday but isn't ready to return to the lineup.
• The Rangers are 17-4 with Chris Gimenez as their starting catcher going into Tuesday night.