Losers of three of their last four games, the Sixers (18-26) have blown late leads against San Antonio and Memphis. They did beat the Atlantic Division-leading New York Knicks on Saturday.
Their next test comes Wednesday night with a home game against the improving Washington Wizards (11-32).
The Sixers simply have not closed out games.
Against the Spurs on Jan. 21, the Sixers held an 82-75 lead with less than four minutes remaining. Then they missed nine of their last 10 shots while San Antonio closed the game on a 15-3 run to win, 90-85.
Against the Grizzlies on Monday, even after blowing a 17-point first-quarter lead, the Sixers were in position to win.
However, they missed their last five shots - some of them open looks at the basket - and failed to score in the final 3 minutes, 5 seconds, blowing a three-point lead in a 103-100 loss.
Collins said that even though the Sixers struggled late, they lost the game in the second quarter, when their poor defense allowed the Grizzlies to rally. Memphis made 14 of 18 shots in the quarter.
"It was those seven or eight minutes that really cost us," Collins said. "They missed shots down the stretch, too. People like to point to the end of games. But it was our defense in the second quarter that hurt us."
Evan Turner scored 27 points against Memphis. He pointed out that the Sixers missed shots late in the game that could have changed the outcome.
But Turner believes that the Sixers are close to turning the corner.
"I think we're getting closer and closer to where we want to be as a team," Turner said. "Once we get over this hump, we'll be rolling. Our past four or five games, we've played with great effort."
Contact John N. Mitchell at firstname.lastname@example.org. Follow on Twitter @JmitchInquirer.