With a place in the third qualifying round of the UEFA Champions League up for grabs, both Celtic and Steaua Bucharest look favourites to advance.
Both sides lifted this trophy in its former guise as the European Cup, but the format of the competition has changed almost beyond recognition since those days.
Celtic became the first British side to conquer Europe with a 2-1 win over Inter back in 1967.
Steaua's success, meanwhile, came more recently, in 1986, when the Romanian outfit overcame Terry Venables' Barcelona 2-0 on penalties after a goalless draw.
Both clubs have fallen well short of those glories in recent times, but the two will feel confident of making the third qualifying round after strong first-leg showings.
Celtic won 2-0 at home to Stjarnan - famed for its choreographed goal celebrations which became a YouTube sensation - while Steaua prevailed by the same scoreline at Trencin.
Should Ronny Deila's men advance, they will take on either Qarabag or Rudar, who played out a goalless first leg. Steaua will come up against Partizan or Dila, with the former winning 1-0 at home last week.
Lech Poznan holds a 2-0 lead over Sarajevo, with the winner earning a third-round tie against Basel.
Molde already has one foot in the next round after it hammered Pyunik 5-0, while Skenderbeu Korce also looks assured of its place after a 4-1 over Crusaders.
Less certain are Milsami, Midtjylland, Videoton and Maribor, who all carry a narrow 1-0 lead into their second legs against Ludogorets, Lincoln Red Imps, The New Saints and Astana.
BATE and Hibernians both won their first legs 2-1, although Dundalk and Maccabi Tel Aviv will fancy their chances of turning the ties around.
Finnish outfit HJK won its first leg 3-1 away at Ventspils and looks in a strong position, while the ties between APOEL and Vardar and Zalgiris and Malmo are scoreless.
Elsewhere, it is similarly all to play for in the tie between Dinamo Zagreb and Fola Esch, which is level at 1-1 after last week's encounter in Croatia.