The Rockets (31-28) blew 17-point leads in each of their last two games, falling 105-103 at Washington on Saturday and 110-107 to Milwaukee on Wednesday.
Harden scored 25 points and Omer Asik had 16 and a career-high 22 rebounds against the Bucks, who won on Monta Ellis' 3-pointer as time expired.
"It was a bad loss," said Chandler Parsons, who added 20 points. "There is no way around it. There is no way we should have lost that game. These are the ones you look back on and these are the ones that cost you so you can't do nothing else now. It is what it is so hopefully we learn as a team and get better from it."
Wednesday's defeat may have also come at a cost. Harden played with a wrap on his left knee after bumping into Ellis in the first half, and Lin twisted an ankle. The Rockets, who continue to cling to the eighth and final playoff berth in the Western Conference, held both players out of Thursday's practice.
"If we took care of business, we could be the seventh or sixth seed right now, and we're not," said Lin, averaging 8.0 points on 32.3 percent shooting over the last three games. "So that really hurts, and we can't expect that other teams are going to give us a chance to climb up the rankings, we have to go do it ourselves."
The Rockets are one-half game behind seventh-place Utah and just a few in front of the ninth-place Los Angeles Lakers.
"We need to focus on the Magic on Friday night," Parsons said. "We can't look ahead, we can't keep looking at the standings. Who cares about the Lakers?
"We control our own destiny right now. So I don't really care what they're doing or who they play as long as we focus on who we're playing."
While Houston has been outscored by an average of 14.2 points during a five-game skid versus Orlando (16-42), these teams haven't met since Dec. 26, 2011.
The Magic, who've gone an NBA-worst 4-29 since Dec. 21, followed Tuesday's 98-84 win at Philadelphia with a 125-101 loss to Sacramento on Wednesday. The Kings shot 54.8 percent and outscored Orlando 56-44 in the paint and 25-8 in transition.
Tobias Harris had a career-high 23 points off the bench while fellow newcomer Beno Udrih posted 14 and eight assists. Both players were acquired from Milwaukee in the J.J. Redick trade.
"Maybe we played hard, but they played harder," Udrih told the team's official website. "We have a lot of talent and potential but we have to bring it every night.
"I put all of my stats on the side when the team losses. I'd rather have zero, zero and zero and the team wins. So hopefully the next game we can be aggressive, play harder on defense and the offense will come."
Harris, averaging 5.4 points over 73 career games, has scored 17.7 on 67.7 percent shooting in three contests with Orlando while wearing No. 12.
"I know that was Dwight Howard's old number, but that's the number that I chose," Harris said. "I know there are a lot of expectations with that number and I'm happy to take on those expectations."