Van Gundy's message to Harris, who was struggling with his shot, was to get out of his own head and just be in the moment.
"He just told me to clear my head and go out there and enjoy the game and just play off everything that happens," Harris said. "That's what I've been able to do and it's been working."
It worked to near perfection Tuesday night. Harris scored 30 points as the Pistons downed the Indiana Pacers 107-83.
Harris was 10-of-11 from the floor, including making seven of eight 3's.
"It's a new approach I have, since I was not shooting as well as I was before, so I'm just letting the game come to me and just try to feed off what the game brings," Harris said. "You go on with a better mindset playing in the game.
"I'll stick with it."
Harris scored 21 points in the first quarter, as the Pistons rolled to a season-high 40 points and a 40-19 lead.
"Obviously, Tobias had a heck of a first quarter, but it all was clicking, on all cylinders," Pistons center Andre Drummond said. "Everybody was scoring."
Drummond finished with 21 points and a game-high 18 rebounds. The entire starting five for the Pacers combined for just eight rebounds and their offensive output was a season low.
"I have no explanation for that, absolutely none," Pacers coach Nate McMillan said. "We're just digging a hole for ourselves."
The victory moved the Pistons (19-14) past the Pacers (19-15) into second spot in the NBA's Central Division and gave the Pistons a 3-1 decision in the season series between the two teams, the first time Detroit had won the season set from Indiana since going 4-0 against the Pacers in 2007-08.
"That's a team we're looking forward to playing in the playoffs, so to get that advantage is huge for us," Drummond said.
Even though it was the sixth straight game that he'd led the Pacers in scoring, Oladipo, who came into the night averaging 25.3 points per game, was held to a season low on the scoresheet.
"You're not going to shut the guy down, but I think we did about as good a job as we could," Van Gundy said. "And then you hope he misses some shots, and he did."
The Pistons lost starting guard Reggie Jackson to an ankle injury in the third quarter. Landing after making a jump pass, Jackson came down awkwardly on his right ankle. He had to be helped from the court and did not return.
"The x-rays were negative," Van Gundy said. "He's got an ankle sprain. We'll get an MRI and see tomorrow where we are."
Jackson finished the night with 13 assists against one turnover in 21:15 on the floor.
"He was unbelievable," Van Gundy said.
Pacers: Indiana's McMillan (539) and Detroit's Van Gundy (503) are two of six active NBA head coaches with 500 or more wins in the league. . The Pacers grabbed a season low in defensive rebounds (21) and total rebounds (26).
Pistons: G Avery Bradley (sore right groin) should be back in action for Detroit's Jan. 3 game in Miami against the Heat. . There's no timetable regarding F Jon Leuer (left ankle sprain). Leuer has resumed shooting but is not yet taking jump shots.
Pacers: Travel to Orlando to face the Magic on Thursday.
Pistons: Play host to the Dallas Mavericks on Wednesday.
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