As giggly and goofy as the Grizzlies often are, there’s a poise that’s atypical given their inexperience. Memphis ranks second in the NBA in clutch winning percentage, going 16-7 in games that are within five points in the final five minutes or overtime. The Grizzlies rank fourth in net rating in those situations, outscoring opponents by 15.7 points per 100 possessions. “We’ve got probably the most clutch performer in the game at our point guard position,” Jackson said following last Wednesday’s win over the San Antonio Spurs. “That does help.”