LeBron James issued a guarantee Wednesday entering Game 4 of the NBA Finals: Don't expect his series-long struggles to continue against the San Antonio Spurs.

Coming off one of the worst postseason performances of his career in Tuesday's 36-point loss to San Antonio in Game 3, James vowed to be far more aggressive amid suggestions the Spurs have knocked him off his game.

James missed 14-of-21 shots and didn't attempt a free throw for only the second time in his playoff career as the Heat suffered their worst postseason loss in franchise history, a 113-77 mauling to fall into a 2-1 series hole.

"As dark as it was last night, it can't get no darker than that, especially for me," James said Wednesday before the Heat's practice at the AT&T Center. "So I guarantee I'll be better for tomorrow (Game 4) for sure. I have to do whatever it takes. I mean, 7 for 21 isn't going to cut it. It's impossible for me to go 7 for 21, shoot 33 percent from the field and not have free throws. You have to figure out ways offensively that you can make an impact."

James acknowledged the Spurs' defensive scheme is far more complicated than it looks, and has contributed to his relative struggles throughout the series. But he also said he needs to be more aggressive and attack instead of reading the defense and waiting for openings. The 50 total points James has scored through three games against the Spurs represents his lowest point total over three straight playoff games since Miami lost to Dallas in the 2011 Finals.

Through three games against San Antonio, James is shooting just 38.9 percent from the field and is averaging 16.7 points, 12.3 rebounds, 7.3 assists and 2.0 turnovers. James has gotten off to sluggish starts in each of the past two games against a Spurs defense committed to packing the paint and giving him as many open jumpers as he wants. He scored four points in the first half of the past two games.

James spent the initial stages of Wednesday's practice working on shots from some of the same mid-range areas where many of his open looks have come against San Antonio. Heat coach Erik Spoelstra said the team has to do a better job of speeding up the game and getting in transition to avoid repeatedly facing a halfcourt defense.

Although James placed much of the blame for Miami's offensive woes on his shoulders, Heat players and coaches said there's been enough ineptness throughout the roster.

Heat teammate Dwyane Wade insisted that James shouldn't be the focal point of criticism for Miami's offensive meltdowns in the series. Wade and Chris Bosh have also had a rough time finding a rhythm against the Spurs, with their respective struggles dating to a brutal seven-game series in the Eastern Conference finals against Indiana.

Neither James, Wade nor Bosh has scored 20 or more points against the Spurs and have combined to average just 43.3 points on 42.1 percent shooting in the Finals.

"We have to try to do our best to make more of our opportunities," Wade said. "We're getting some shots that we want. You know, it's everybody. Obviously, it starts with us three. We have to do a better job of being that quote, unquote, Big Three and leading our team."