Al Hilal show no signs of FIFA Club World Cup hangover as favourites advance into AFC Champions League quarterfinals

Reigning champions Al Hilal kept their hopes of a successful title defence alive as they beat Shabab Al Ahli 3-1 on Monday to advance into the quarterfinals of the 2022 AFC Champions League campaign. Matthew Ashton - AMA/Getty Images

More than ten months after the campaign began, the AFC Champions League's West Zone finally got to its business end on Sunday and Monday as what will be a whirlwind knockout round began with the last-16 ties.

With Asia's premier club competition in a transitional season as it shifts to a September-to-May calendar, the 2022 campaign will extend to this May - which explains why the round of 16 in the western half of the competition is only just taking place now.

But it was business as usual for some of the tournament's usual suspects as a handful of favourites advanced -- albeit with varying degrees of comfort -- into the quarterfinals, which will be held on Thursday before Sunday's semifinal determines who meet Japan's Urawa Red Diamonds -- the finalists from the East Zone -- in the decider later this year.

Here, we take a look at four things we learned from the round-of-16 ties that took place over the past two days.

Zakaria emerges as hero as Al Duhail toil for quarterfinal berth

Much of Qatari giants Al Duhail's credentials as genuine contenders stems from their vaunted attack, boasting the tournament's current top scorer Edmilson Junior alongside Qatar star Almoez Ali, Kenya international Michael Olunga and South Korea playmaker Nam Tae-hee.

With 17 goals in the group stage -- the second-best record in the West Zone -- it is impossible to deny that their firepower up front has been a key driving force.

Yet, on Sunday, as they struggled to find a way past stubborn compatriots Al Rayyan, in a game which ended in a 1-1 draw after extra-time, it was their last line of defence that grabbed the limelight.

Still only 23, Al Duhail goalkeeper Salah Zakaria had already produced a series of fine saves throughout the match when he emerged as the hero of the penalty shootout by saving Al Rayyan's 7th attempt Mouafak Awad, securing a hard-fought place in the last eight.

Al Shabab can challenge with Banega leading the way

Al Shabab may not boast the same stature as some of Saudi Arabia's more-illustrious teams, but they are still a club that have won six Saudi Pro League titles previously.

On the continental stage, however, they have only once reached the semifinals of the ACL although -- in their first appearance since 2015 -- they are fast emerging as legitimate challengers.

While it was not exactly a faultless display on Sunday, they were ultimately largely untroubled in a 2-0 triumph over Uzbekistan's Nasaf Qarshi -- with goals coming from Hussain Al-Qahtani and Ever Banega.

In the experienced Banega, an European football veteran with notable spells at Valencia, Sevilla and Inter Milan, Al Shabab boast a genuine game changer who make a difference -- as he showed when he scored their second of the evening with a precise 25-yard drive on his weaker left foot that found the back of the net of the post.

Less-illustrious Foolad flying the flag for Iran

Iran's ACL challenge has traditionally been led by the likes of Sepahan, Persepolis and Esteghlal and, while all of them have gone far in the competition, it is remarkable that such a continental giant has yet to produce a title-winning team.

With Persepolis and Esteghlal disqualified from this year's due to a failure to meet the Asian Football Confederation's licensing regulations, and Sepahan eliminated in the group stage, it is now down to Foolad to fly the flag for the Iranians.

Foolad are not exactly strangers when it comes to competing on Asian football's biggest stage having featured in four previous editions, and their experience came to the fore as they grinded out a 1-0 victory over Al Faisaly on Monday.

With some seasoned campaigners to call upon, headlined by ex-Iran captain and former Fulham man Ashkan Dejagah, Foolad could just go on to cause an upset or two even if they may not be as heavily-fancied as the West Zone's other quarterfinalists.

Al Hilal show no signs of Club World Cup hangover

Having caused quite a stir by reaching the final of the recent FIFA Club World Cup, before ultimately succumbing to Real Madrid in a 5-3 thriller, Al Hilal showed no signs of a hangover as they comfortably negotiated past their round-of-16 test with a 3-1 win over Shabab Al Ahli.

While the reigning SPL champions boast a whole host of Saudi Arabia stars, many of whom played pivotal roles in an impressive FIFA World Cup campaign at the end of last year, a main strength also lies in their outstanding foreign contingent.

Former Manchester United striker Odion Ighalo, South Korea defender Jang Hyun-soo and Argentine playmaker Luciano Vietto -- who scored twice against Real -- got the goals on Monday to secure straightforward progress into the quarters.

And Al Hilal will only get better as they welcomed back Salman Al-Faraj from an injury that saw him miss Saudi Arabia's last two games at the World Cup, with their talismanic playmaker and captain returning to the field as a 75th-minute substitute.