OKLAHOMA CITY — The Philadelphia 76ers were always going to have a struggle against the Oklahoma City Thunder. And true to that, the Sixers emerged from Sunday afternoon with a 129-104 loss to the reigning NBA champions.

That’s not the loss that currently smarts for Philadelphia. The 76ers should have found a way to beat the Brooklyn Nets on Tuesday. They were a better team on paper than the Chicago Bulls, but lost to them on Friday night. They didn’t take care of business in the games in which they needed to, which is of paramount importance in the NBA.

So, the Sixers own a three-game losing streak as they prepare to face the Memphis Grizzlies Tuesday night.

Philadelphia hasn’t won four consecutive games since the beginning of the year, but it also hadn’t lost three straight until now. It’s given the Sixers their biggest challenge of the season. They are reeling of sorts; they aren’t playing well on the aggregate. And they are amid a five-game road trip that doesn’t feature the right opponent that can stop a losing streak.

“We didn’t take care of business against Brooklyn and Chicago,” 76ers point guard Tyrese Maxey said. “But at the same time, we have to let those losses go. We have to look forward. We have three games remaining on this trip, and we have to figure out a way to win them all. I think we’re in the right mindset in the locker room. I think everyone is in good spirits. We have two games out west before we get back to our side of the country and go back to New York (to face the Knicks).”

The Sixers are not as good a basketball team as the Thunder. Maybe we are being a bit obvious in that statement. So, Sunday’s outcome boils down to OKC locking in defensively in the second half, turning a 64-62 halftime lead into a blowout by the end of the third quarter and then cruising to a win.

Nonetheless, that doesn’t mean there haven’t been some issues creeping in over the last week or so. The biggest and most consistent is that the Sixers continue getting cooked during the third quarter. That’s happened all season, regardless of the competition. In terms of basketball, it’s the most alarming weakness Philadelphia has, and it’s been something the 76ers haven’t been able to get a handle on.

The Sixers have been a good fourth-quarter team, yes. However, against good teams like the Thunder, a bad third quarter will put you into such a deep deficit that the fourth quarter won’t matter. This is a Philadelphia franchise aiming to enter the postseason and make an impact. The Sixers can’t do that while consistently playing bad basketball for a significant amount of minutes. If there is anything to take from Sunday afternoon’s loss, it’s how quickly a good team can take a two-point halftime lead and extend that lead to over 20 points, if the 76ers don’t do the right things.

“We had a big amount of turnovers, and that put our defense in a lot of trouble,” Philadelphia head coach Nick Nurse said. “There were about 14 in the second half, and that’s just way too many. They turned up the pressure defensively, but about a good 10 of those were our fault. We didn’t play well enough on the defensive end. We never got our defense established in the second half. It was a rough game for us in terms of keeping the ball in front of us.”