#3 Barcelona 2:0 Manchester United
(2008-09 Champions League Final)
After meeting twice in the 2007-08 UEFA Champions League, Cristiano Ronaldo and Lionel Messi renewed acquaintances again in the next edition of the competition when Manchester United locked horns with Barcelona in the final.
While United looked to become the first team in the Champions League era to successfully defend their title, a rampaging Barcelona under Pep Guardiola had other ideas.
Barcelona captain Carles Puyol, playing in an unfamiliar right-back role due to the unavailability of Dani Alves, capitalized on a moment of hesitation in the United left-wing to devastating effect.
After an Edwin Van der Sar goal-kick was aimed in the direction of Cristiano Ronaldo, Puyol reclaimed possession burst forward and teed up Samuel Eto'o, who exchanged passes with Lionel Messi before opening the scoring.
Cristiano Ronaldo was arguably also at fault for Barcelona's second goal, but Lionel Messi's best in the game was yet to come. When Patrice Evra's poor clearance went straight to Xavi, Ronaldo could have tracked back with vigor and tried to dispossess the player but didn't.
Moments later, the master passer threaded an inch-perfect cross to an unmarked Lionel Messi in the center of the United box as Rio Ferdinand stood transfixed and was caught ball-watching. The unmarked 5' 7" Argentinian leapt in the air and sent a looping header beyond the reach of Van der Sar.
Talking about that goal in a later interview, Messi remarked:
"It was hard to imagine that I was going to score with my head with (Rio) Ferdinand standing near me, but I didn't really have a marker - the ball came into the centre, and I was there to meet it."
With the 2-0 win, Guardiola's men became the first Spanish team to win the continental treble as Barcelona completed one of the finest-ever seasons in club football.
#4 Real Madrid 0:2 Barcelona
(2010-11 Champions League Semifinal First Leg)
After three Champions League meetings with Lionel Messi's Barcelona while he was at Manchester United, Cristiano Ronaldo met the diminutive Argentinian for the fourth time in the competition with Real Madrid when the record champions locked horns with the Blaugrana for a place in the 2010-11 final.
In an ugly ill-tempered game at the Santiago Bernabeu, chances were at a premium for both sides as Cristiano Ronaldo, who was often the lone Madrid player up front, displeased with his team's ultra-defensive mindset.
After Pepe was shown a straight red card for a foul on Dani Alves at the hour mark, Barcelona made their numerical superiority count 14 minutes from time. Lionel Messi converted an inch-perfect cross from Ibrahim Afellay to open the scoring.
However, the Argentinian was not yet done for the night. Producing a moment of sublime masterclass, Lionel Messi dodged three Real Madrid defenders, and then two more, before slotting the ball into an unguarded net after drawing Iker Casillas forward, as Barcelona took a commanding 2-0 lead to the second leg at Camp Nou.
#5 Barcelona 1:1 Real Madrid
(2010-11 Champions League Semifinal Second Leg)
A week after winning by two unanswered goals at the home of their fierce rivals, Barcelona withstood some early Real Madrid pressure to hang on to their aggregate lead and reach their second Champions League final in three years.
Unlike in the first leg at home, the visitors were enterprising in the early exchanges, with Cristiano Ronaldo at the forefront of Real Madrid's promising attacking play. But it was Barcelona who further extended their advantage when Pedro converted an Andres Iniesta pass to open the scoring.
Real Madrid now needed to score four unanswered goals. Far from being crestfallen, Jose Mourinho's men rose to the challenge and equalized almost immediately courtesy Angel Di Maria. However, there were to be no more goals on the night as the two-goal defeat at home proved too steep for Madrid to overcome.
In the process, Barcelona became the first (and till date the only) club to deny Cristiano Ronaldo in five Champions League games. The Portuguese maestro has not scored in four UCL games apiece against Benfica and Lille respectively.
Barcelona would go on to win their second Champions League title in three years by beating Manchester United 3-1 in the Wembley final.