Reggie Miller, the great shooting guard for the Indiana Pacers, used to call it "winning time," the portion of a game when the best step up and get the job done. It's a concept that is pretty easy to talk about - and almost impossible to actually do. The reason we call sportsmen like Miller, or Muhammad Ali, or Jack Nicklaus "great" is because when the pressure was on, they were able to summon up that focus, make that basket, evade that jab, or sink that putt, with the entire world watching.

This weekend, two teams took giant steps towards securing league titles. Both can arguably claim to be the best in European soccer, and both will meet in just under three weeks time to settle the matter. Both have demonstrated all season long that the mental part of any sport - the part that cannot be coached, only reinforced - is the difference between owning that winning time and going home.

Manchester United and Barcelona are now a single point away from claiming their respective league titles. That they will win them is a given. Over the past two weeks, the English and Spanish sides have shown a resilience that their rivals have lacked, and it is that steel that has carried them to where they are.

United downed Chelsea on Sunday in a coolly efficient fashion that should end all talk of who the best team in England truly is. Taking just 36 seconds to go ahead behind a goal from Javier "Chicharito" Hernandez, United broke Chelsea like cheap china. The difference maker on a team full of stars, no less, was not Wayne Rooney: It was Park Ji-Sung, a squad player who has shown a knack for seizing big games.

Park, tireless in midfield, set up the first goal and proved so distracting that Chelsea manager Carlo Ancelotti was forced to remove the two players he tortured at the half: $33m signing David Luiz and midfielder Jon Obi Mikel. The final 2-1 scoreline, padded by some lenient refereeing and a poached goal by Frank Lampard, in no way reflects what was truly a domineering performance by the Red Devils.

United didn't place a hand on the trophy with a single game, mind you. In fact, they have been forced to grind out more than their share of results on the backs of squad players like Park, Michael Carrick and Chris Smalling and can only finish with a maximum of 82 points, the lowest total since the 2000-01 Premier League season. They dropped more than their fair share of points on the road and were forced to stumble through an unconvincing stretch that saw them rocked by losses to Chelsea and Arsenal as both teams steadily gained on them.

The difference between United and their rivals, however, is belief, and for that, one has to look no further than their manager, Sir Alex Ferguson. Ferguson, who indeed has money to spend and a wealth of talent at his fingertips, has nonetheless convinced every man in his lineup that not only are they capable of winning games, but that they will win games. How else to explain Darron Gibson's performance against Schalke after the bitter hazing he has taken from some of the club's fans? Or the blossoming of mercurial and stormy types such as the Da Silva twins or Nani? Or the continued magnificence of Ryan Giggs and Edwin van der Sar, players that other clubs might have put to pasture years ago?

For proof, look no further than how Chelsea started their second half Sunday. Absent from the lineup were the men they spent $110m on in January (Fernando Torres, in the biggest game of his short Chelsea career, wasn't even trusted enough to start). Say what you want about the lucre of Chelsea, but all the money in the world cannot buy confidence, and even this Blues team that had taken 25 of their last 27 points to come back within touching distance of the top had no idea how to win this game.

Or look at another London club, Arsenal, which dropped an embarrassing match at Stoke, 3-1, earlier the same day. How is that a club that once had a realistic chance of winning a couple of trophies came so far off the rails? Ask chastened manager Arsene Wenger who admitted after the latest disaster that his young side is mentally weak. How weak? His captain, Cesc Fabregas, watched from the stands with a "thigh problem" as the official reason - and the real reason is that he, like half the team, has already checked out.

Barcelona are just as impressive, having come through one of the toughest gauntlets imaginable: playing their bitter rivals four times in 18 days with three trophies on the line. There, manager Pep Guardiola has taken a largely homegrown team of talent and molded them into what has to be considered the greatest club of their era. Yes, they have talent to spare. But in shooting down Real Madrid in the two races that matter - the Champions League and La Liga - they have shown that desire can trump all other concerns.

Consider that the heart of their squad has been playing high-level soccer for 36 straight months, winning a European Championship and a World Cup in that time and now looking as if they will add their third-straight league title. They may win their second European Cup inside three years, and under Guardiola have already completed the first treble in Spanish soccer history, just two seasons ago. This is a brutal, punishing schedule that has seen the heart of their squad have at most four months off in that span. And yet, the desire remains unabated: They have lost just twice in league play this season, and that should say it all.

Their only rivals are locked in bitter recriminations. Despite winning a trophy, the Spanish Cup, their indisputably talented manager Jose Mourinho is at war with the club, the press, and some of his players. Elsewhere, he has demonstrated that he can win. But he hasn't yet convinced this Madrid team of that, as we saw in the Champions League. There, he was tentative and conservative, his negative tactics acknowledging that his team could not play open soccer with Barcelona. The result was painful to watch.

The next chess match takes play in London, where United may well have an advantage. Neither team will fear the other, and both squads will believe they will win. If it is half as compelling as the drama we've seen in their leagues this season, we fans will be the true winners.

Jamie Trecker is a senior writer for FoxSoccer.com covering the UEFA Champions League and the Barclay's Premier League.