There are no easy fights when you're ranked as the number-one challenger.

That should be obvious. Aside of actually being world champion, sitting first in line is where everyone wants to be.

Tim Tszyu is still in that spot after his dramatic victory over the game but ultimately out-gunned Terrell Gausha, maintaining his momentum towards a world title shot as he moves to an unbeaten record of 21-0.

Yet, the way Gausha hurt Tszyu, knocking him down in the first round with a brilliant overhand right off the back of an accurate jab, does raise some questions.

It's not a huge surprise that Tszyu looked vulnerable for the first time in his career during his US debut.

Boxing is an unusual sport in as far as you're never sure where you stand until you see two people in the ring for the first time.

Progression through the boxing ranks is only possible by exposing yourself to risk — that's part of its allure.

Not only that, but the only time a fighter can genuinely test themselves at a higher level is in front of the cameras and fans. 

There's nowhere to hide.

For Tszyu, his first step into the American market was fraught with risk.

Not only because he was fighting against an opponent with an impeccable amateur pedigree with a handy world ranking, but that he did so outside of the comfort zone that Australia and all its trappings provides.

At home, he is a star.

In the US, he's just another name. 

This is where Tszyu wants to be though, fighting prime-time in boxing's biggest market, a proving ground where his dad, Kostya fought 14 times, including winning his first world title against Jake Rodríguez in Vegas in 1995.

It's OK for Tszyu to have been slightly overawed by the experience — prime-time in the USA is quite different to midweek in Australia.

Rather that happen now than in a world-title fight, when the level goes up another notch or two.

"In the first three rounds, everything's flash, everything's quick," Tszyu explained ringside after the fight.

"You sorta blink and you're down and you think, f***, how did that happen?"

It happened because Gausha, a hardy pro who may have been underestimated by some in the Australian press, used a perfectly timed jab and bludgeoning right to take Tszyu to places that he'd never been before.

When Gausha nailed Tszyu's chin with a sweet right that sent the Aussie tumbling to the canvas, there would have been a sharp intake of breath from most of those watching.

"There was definitely some shit thoughts going through your head at that time," Tszyu admitted after the fight.

If that was the first lesson, the second should be that defence is a valuable attribute in boxing.

Tszyu's tendency to try to walk through shots to get into a position to make his own land has not been exposed in the way Gausha did.

But this was a step up and the Australian's lack of head movement as he probed for an opening kept Gausha in the game for longer than it should have.

The shots that Gausha landed with his right throughout the fight is another thing that future opponents will take note of, with Jeff Horn highlighting it as something that could make Tszyu vulnerable.

Gausha also made it difficult for Tszyu to really wind up and use those tenderising body shots to his best advantage by some subtle positioning in their exchanges — the sort of defensive work that doesn't feature in highlight reels but is invaluable in these tough slugfests at the highest level.

However, despite those issues, those body shots still came, buckling Gausha in the fourth and fifth and keeping the American honest right up until the final bell, as Tszyu showed a toughness that speaks of his fighting maturity. 

That he did so off the back of an illness-ravaged training camp is again a positive sign.

"For the two weeks I was here in America, it was hard work," Tszyu said.

"Three days before the fight I was coughing like a dog.

"It was horrible. I couldn't breathe, it's still in my lungs."

Yet, despite facing that adversity, in his own words, Tszyu still "got the job done against a world-rated opponent".

Tszyu also said making the weight at 70kg was "a problem" this time around, not the first time he's said shredding for the weigh-in was becoming an issue.

That makes his next fight, which will likely be against the winner of Jermell Charlo and Brian Castaño's unification rematch in May, his last before moving up into the bearpit that is the middleweight division — where any and all of the weaknesses highlighted by Gausha will be exposed tenfold.

Tszyu said after the fight that he needed to work on "everything" before he steps foot in a ring again to realise his dream of becoming a world champion.

That may be so, but the lessons he's learned from this toughest of sporting schools, should stand him in good stead for when that next challenge comes.