Jake Shields and 5 of Georges St-Pierre's Toughest Opponents

According to UFC welterweight champion Georges St-Pierre in a video on the UFC's Facebook page, Jake Shields is probably the toughest opponent he's ever faced.

The former Strikeforce middleweight champion stood toe-to-toe with the French Canadian for five grueling rounds in their championship bout at UFC 129.

Before facing Shields, St-Pierre hadn't even lost a round in four years.

He wasn't able to come away with a victory, but Shields proved that he was one of the top pound-for-pound fighters in the world and certainly worthy of a UFC title shot.

Fans have come to expect dominance from St-Pierre, who has virtually destroyed every upper-echelon foe thrown his way.

Even with his everlasting dominance, there have been moments in St-Pierre's UFC career where he's faced adversity.

Join Bleacher Report as we reminisce on Georges St-Pierre's toughest opponents.

Matt Serra

Matt Serra would be the last person anyone would ever expect to be considered as one of Georges St-Pierre's toughest opponents.

After winning season four of the "Ultimate Fighter," Serra was awarded a welterweight title shot at UFC 69 against the seemingly invincible St-Pierre.

Fans and media took the bout as a circus match that would undoubtedly end with the French Canadian having his hand raised.

In perhaps the most stunning upset in the history of the sport, Serra stopped St-Pierre in the first round with a vicious TKO.

The loss brought St-Pierre, who had just defeated Matt Hughes for the UFC title, back down to earth and taught him that no one is invincible. On any given night, all that you've worked for can be taken away by anybody, regardless of the odds.

St-Pierre made a lot of changes in his career after the loss. Along with changing managers, he became smarter about the kinds of friends he surrounded himself with.

At UFC 83, St-Pierre avenged his loss to Serra and reclaimed the welterweight title. Tough opponents come in unexpected places, and Serra certainly deserves props for temporarily halting the seemingly unstoppable St-Pierre war wagon.

Matt Hughes

Georges St-Pierre has remained candid in admitting that UFC Hall of Famer Matt Hughes has always been his idol.

In his first bout with Hughes at UFC 50, St-Pierre started off strong, but he faltered towards the end of the first round by attempting a kimura from bottom without securing Hughes' leg.

Surprised by the rookie-like mistake, Hughes quickly took advantage by countering the kimura attempt with an armbar, which forced St-Pierre to tap with only a second left in the round.

The second bout went much different, as a much more mature and composed St-Pierre stepped up to challenge Hughes at UFC 65.

Hughes had no answer for the technical superiority and speed of St-Pierre's standup. The most surprising part of the bout was Hughes' inability to secure a takedown.

After getting lit up in the first round, Hughes saw his reign of dominance come to an end in the second after eating a St-Pierre high kick.

The second bout felt like a passing of the torch, but it wouldn't be the last time these two adversaries would step into the octagon against one another.

The rubber match took place a year later at UFC 79, where St-Pierre completely separated himself from Hughes by dominating once again and picking up the second round submission victory.

The rivalry ended the same way it began––with an armbar.

Josh Koscheck

Georges St-Pierre has never faced an opponent more mentally draining than Josh Koscheck.

The two first met at UFC 74, where St-Pierre defeated Koscheck in a rebound victory after dropping the welterweight title to Matt Serra.

While St-Pierre picked up the convincing unanimous decision, the outcome wasn't nearly as dominant as some expected it to be.

Some even scored the first round for Koscheck, who managed to secure a takedown on the acrobatic St-Pierre.

The bout quickly turned around in the second and third rounds, as St-Pierre found his rhythm on the feet and began nabbing takedowns of his own.

After the first fight, the two crossed paths three years later as coaches on season 12 of the "Ultimate Fighter," where Koscheck did everything in his power to get under St-Pierre's skin.

His efforts proved to be futile, as St-Pierre dominated the blonde-headed villain in front of his hometown fans in Montreal, Quebec, at UFC 124.

Jake Shields

Heading into his UFC 129 superfight with Georges St-Pierre, Jake Shields had a lot going for him.

Considered as one of the top pound-for-pound fighters in the world, Shields was coming off huge wins over Dan Henderson and Martin Kampmann.

He was a world class wrestler who had enjoyed success at 185-pounds. His Brazilian Jiu-Jitsu prowess is known all over the world, as he is a black belt under Cesar Gracie and a 2005 Bronze medalist at ADCC.

Hardcore fans had been looking forward to the Shields and St-Pierre bout for a very long time.

When the fight actually went down, it didn't unfold the way many expected. St-Pierre kept the fight standing and bested the exchanges for five rounds, but Shields was able to outpoint the French Canadian on more than a few occasions.

In the end, St-Pierre was awarded the unanimous decision, but he left the arena that night a little more busted up than fans are used to seeing him.

B.J. Penn

When considering the toughest opponent Georges St-Pierre has ever faced, B.J. Penn has to be at the top of the list.

At UFC 58, Penn left St-Pierre a bloody mess after only one round of action.

He utilized a stiff jab and slick head movement to pick St-Pierre apart in the standup exchanges.

When the bell sounded, St-Pierre went back to his corner with a broken nose and a badly busted up right eye.

He rebounded in the second and third rounds by relying more his wrestling. Despite a valiant effort, Penn wasn't able to shrug off enough takedowns to sway the minds of the judges, who handed St-Pierre the split decision.

After the bout, Penn went on to lose to Matt Hughes and drop back down to the lightweight division, where he defeated Joe Stevenson for the world title.

It would be champion versus champion when Penn returned against St-Pierre at UFC 94.

There was definitely more at stake in this iconic championship bout, but the outcome produced a much more definitive result.

St-Pierre dominated Penn from start to finish, and the Hawaiian's corner was forced to thrown in the towel at the end of the fourth round.