Sixteen sides representing seven countries do battle as the AFC Champions League knockout stage commences on Tuesday and Wednesday. Among the group are a host of former winners aiming to impress.

Many eyes are on the champions' clash between Seongnam FC and Guangzhou Evergrande with each side seeking to emulate their old, continent-conquering feats. 2006 champions Jeonbuk Motors entertain Beijing Guoan confident of drawing first blood, while 2008 winners Gamba Osaka travel to Korea Republic hoping for a good start against FC Seoul.

Elsewhere, Al Sadd do battle with compatriots Lekhwiya in an all-Qatari affair and the same can be said of inaugural champions Al Ain who will look to win at fellow UAE league side Al Ahli.

The match
Seongnam FC-Guangzhou Evergrande
On paper, this pair looks well-matched, with each having progressed beyond the group phase on more than four occasions including clinching the silverware once. But those following the teams closely are aware of the gap that exists. Seongnam, or the Citizens' Team as they are known by their faithful, are an unfancied side with few high-profile players - none of the team represented Korea Republic in January's AFC Asian Cup. Guangzhou, however, features a series of Chinese internationals as well as eye-catching imports such as tournament top-scorer Ricardo Goulart.

It is then no surprise that the encounter is seen as David versus Goliath even among the Korean media. However, Guangzhou coach Fabio Cannavaro is clear that they write Seongnam off at their peril considering the hosts' impressive home record - Kim Hak-Bum's side lost just once out of 11 outings at home in all competitions this season. A 1-0 home defeat of Ulsan Hyundai provided Seongnam with a timely boost, while Guangzhou will look to reproduce the form that saw them thrash Shanghai Shenxin 6-1 recently.

The other attractions
Another Korean-Chinese clash pits Jeonbuk Motors against Beijing Guoan. The K-League hosts are confident of extending their dominant record against Chinese sides, having defeated Shandong Luneng both home and away. Though, they should keep wary of the visitor's solid defensive-line which has conceded just three goals. With defender and captain Xu Yunlong back from injury, Beijing enter the match seeking their maiden away victory against K-League sides.

Suwon Bluewings enter their home game against Kashiwa Reysol with a score to settle, having suffered a disastrous 6-2 loss against the Japanese in a group game in the 2013 edition. Seo Jung-Won's hosts can take heart from a pair of group victories against Urawa Red as they seek to avenge their previous loss. However, it is the visitors that boast an undefeated record against K-League sides having won four and drawn two out of six past meetings.

Even a 1-1 draw against Kawasaki Frontale at home is unlikely to dent Gamba Osaka's hopes against hosts FC Seoul as the Japanese champions are hoping to reach the last eight for the first time since being crowned Asian kings seven years ago. The home side have, meanwhile, recorded a pair of consecutive wins including thrashing Chunnam Dragon 3-0.

In the continent's west, Lekhwiya take on Al Sadd hopeful of continuing their fine form this season, having emerged as Qatar champions at Al Sadd's expense. In the process they lost the first leg 3-0 but won the return 1-0 which helped pave the way to the league title. But generally, Al Sadd hold a slight edge with two more victories from all seventeen previous meetings.

Al Ahli entertain Al Ain as they seek to emulate heroics from the 2013/14 season when they defeated their rivals home and away en route to the UAE league title. A 1-0 victory in the Super Cup final helped cement their confidence, although they grabbed just a point over two legs in the league as they conceded the championship to the opponents.

Elsewhere, it is Iran versus Saudi Arabia as Persepolis welcome Al Hilal. The hosts have turned the Azadi stadium into a fortress having won all three home games including dispatching Saudi side Al Nassr 1-0. Elsewhere, first-timers Naft Tehran tackle visiting Al Ahli expecting to continue their fairytale run.

Player to watch
Beijing Guoan will look to the goal-scoring knack of Dejan Damjanovic as they travel to Jeonbuk. The 33-year-old Montenegrin forward completed a brace as the capital side defeated Liaoning 2-0 on Saturday. Aside from his prolific form, Damjanovic is a revered name in Korea Republic, having finished as K-League top-scorer on three occasions with FC Seoul.

The stat
- Naft Tehran have emerged as the sole debutants in the knockout stage, while Korea Republic are the only country with all four teams through to the Round of 16.

What they said
"We got 12 points (in the group stage), which is better than we achieved in the previous edition. This means that things will be promising in the next period," Al Ain coach Zlatko Dalic

Round of 16 first-leg fixtures:
May 19 & 20
Jeonbuk Motors-Beijing Guoan
Suwon Bluewings-Kashiwa Reysol
Persepolis-Al Hilal
Al Sadd-Lekhwiya
Seongnam FC-Guangzhou Evergrande
FC Seoul-Gamba Osaka
Naft Tehran-Al Ahli
Al Ahli-Al Ain