WALTHAM, Mass. -- The Boston Celtics will make their pitch to free-agent superstar   Kevin Durant  on Saturday evening, but their warm-up appears to have gone well. The Celtics emerged encouraged after meeting with free-agent forward Al Horford on Friday night, a league source confirmed. The Vertical reported Saturday that the Celtics and Wizards have emerged as front-runners for Horford, while the Atlanta Journal Constitution reported that Horford has informed the Hawks that he will make a decision about his future by Saturday evening. That could be ideal timing for the Celtics, whose presentation to Durant would be a bit more intriguing with Horford in the fold. The Celtics are considered a long shot in the Durant sweepstakes because they are not an obvious title contender such as the Thunder, Clippers and Spurs, who have already met with Durant this week. Boston's pitch is expected to detail to Durant the reasons why the Celtics' future might be...