Suddenly, the Thunder has a new issue.

And, no, this latest problem is not a natural sign of the team's progress.

It's more like Oklahoma City's leading cause for concern.

Already saddled by fundamental flaws such as turnovers, rebounding and an inability to knock down open shots, the Thunder must now attempt to erase a seemingly insurmountable 3-1 series deficit to the Memphis Grizzlies while its star player is disappearing down the stretch.

For as much as Kevin Durant has done to carry the Thunder in the absence of Russell Westbrook, he simply hasn't been the closer his team needs him to be.

Durant's production has dipped in the final period in each of the past three games, culminating with a scoreless overtime session in Monday night's Game 5. As Durant struggled, missing all five of his field-goal attempts in the extra period, so did his team. The Thunder went 1-for-8 in overtime and was outscored 9-3 before walking out on the wrong end of a pivotal six-point decision.

Now, with the Thunder on the brink of elimination entering Wednesday's Game 5 inside Chesapeake Energy Arena, little else seems to matter more than Durant reverting to the clutch performer he's established himself to be.

In this scintillating series with the Grizzlies, Durant has averaged 30.8 points, 11 rebounds, 6.8 assists, 1.5 steals and one blocked shot while playing 45.1 minutes and shooting 46.2 percent. But those numbers belie Durant's effectiveness in the closing minutes. And thanks to three straight losses, the last time he rose to the occasion feels like many moons ago, though it's been only 10 days since Durant's late dominance in Game 1.

In the fourth quarter and overtime since Game 2, Durant is averaging just 5.6 points on 29.2 percent shooting. He's averaged only one assist over that span.

On Monday night, Durant scored a mere five points on 2-for-13 shooting in the fourth quarter and overtime. In Game 3, Durant scored just two points on 1-for-4 shooting in the fourth quarter of another six-point defeat, making him 3-for-17 in the fourth quarter and overtime over the past two games.

The final five minutes have been more horrendous.

In this series, Durant has averaged only 3.3 points while shooting just 35.3 percent in crunch time, or the last five minutes when neither team is ahead by more than five points.

In the last three games, Durant's numbers in that window have dipped to 1.7 points per game on 16.7 percent shooting.

Worse, during crunch time, Durant has gotten to the free-throw line only four times in this series.

Many think Durant's mounting minutes are taking a toll.

“He is playing a lot of minutes,” said Thunder coach Scott Brooks. “But he has to. He has to play, and he can handle them. But he has to be able to manage through. But he's been carrying this team very well. He's putting us in positions to win every single game.”

But not delivering.

Several factors are contributing to the disappointing results, starting with Durant not getting many easy shots.

Only 10 of Durant's 33 shots in the fourth quarters and overtime in this series have come from within nine feet. It's a credit to a stingy and disciplined Grizzlies defense. Memphis has made Durant play in a crowd and see multiple defenders each time he catches the ball and thinks about making a move.

But there also is a key difference between Game 1 and the last three contests.

Tony Allen.

Since Game 2, the Grizzlies have assigned their best perimeter defender to Durant for the majority of the final nine minutes. Contrary to what Memphis coach Lionel Hollins was selling after Game 1, when he played his pit bull only 1 minute, 24 seconds in the fourth quarter, Allen can indeed still contain Durant.

In the last three games, Durant has shot 40.5 percent with Allen on the floor and 52 percent with him on the bench.

“He's a good defender, but they're team, they do a great job,” Durant said. “They're not going to let me play one-on-one with anybody. But he's tough because he's small and he gets up under you and he's good at contesting shots.”