Bayer Leverkusen tightened their grip on second place in the Bundesliga as they cruised to a 2-0 victory at struggling Holstein Kiel on Saturday while Serhou Guirassy hit four goals as "euphoric" Borussia Dortmund routed Union Berlin 6-0.

Reigning champions Bayer Leverkusen eased past struggling Holstein Kiel 2-0 with a goal and an assist from Amine Adli in the Bundesliga on Saturday to close the gap on leaders Bayern Munich to five points.

Bayer Leverkusen's dwindling hopes of defending their Bundesliga title must not be derailed again by promoted Holstein Kiel, coach Xabi Alonso said on Friday. October's 2-2 home draw with Kiel was an early blow to Leverkusen and Bayern Munich have gone on to establish an eight-point lead at the top.