This time, Betancourt yielded singles to John McDonald with one out and Gerardo Parra with two outs before Hill's 26th homer of the season dropped the Rockies to 63-98.
At least the Rockies could take solace in yet another solid start from right-hander Jhoulys Chacin, who struck out four in five scoreless, three-hit innings.
The Rockies expected Chacin, who had a strong beginning to last season but deteriorated in the second half after struggling through forearm tightness, to stride toward stardom. However, he struggled to a 7.30 ERA in five starts before going on the disabled list with a nerve issue in his chest.
Now, Chacin looks more like the pitcher the Rockies hoped to have. He finished the season with a 4.43 ERA, and gave up zero or one run in six of his nine starts since his return.
"I felt really good today," Chacin said. "In the first two innings, I couldn't get the ball down and was throwing the ball up. But I got my rhythm and got my feeling with all my pitches. I felt really fresh, like I didn't pitch today. That's a good sign going into the offseason."
Chacin said he will try to maintain his groove with a couple of starts in the Arizona Instructional League and 6-to-7 in the Venezuelan Winter League.
"For Jhoulys Chacin to finish up in the manner in which he did, you have to be extremely encouraged by that," Rockies manager Jim Tracy said.
The Rockies were in position to take their first road series win since Aug. 20-23 against the Mets, but couldn't do it because of two homers accounting for all of the D-backs' runs.
The Rockies led, 1-0, before McDonald homered for two runs off Guillermo Moscoso in the seventh.
"I was just trying to put a good swing on it and he threw a strike," McDonald said. "I was trying to stay up the middle. I'm not a home run hitter so fortunately I got that ball to carry a little bit for me. "
Moscoso even being in the game at the time was a story in itself.
With runners at first and third and two out in the top of the seventh, Tracy allowed Moscoso, who had pitched a scoreless sixth, to bat. He struck out. The bench has been shortened by injuries, and Tracy said after the game that after using seven relievers in Monday night's long contest, Colorado's bullpen was short.
Jordan Pacheco had two hits, including a two-run double to put the team ahead in the eighth, lifting his batting average to .306, tops among NL rookies.
He is also in line for a top-10 finish in the league. One plate appearance in Wednesday's finale will give him the 502 he needs to officially qualify for the leaderboard. It will be the highest finish by a Rockies rookie. Todd Helton finished 12th with a .315 average in 1998.
Tyler Colvin also doubled twice, and DJ LeMahieu and Jonathan Herrera had two hits apiece.
But Hill spoiled the night by providing the second walk-off homer of the season for the D-backs (81-80), who assured themselves of a .500 finish.
"It's a great feeling," Hill said. "Any time you can produce to help your team win, but especially in a situation like that. That's what you think about when you're a little kid when you're playing on the street."