By Paul Giblin

MOSCOW, June 30 (Xinhua) -- The second day of knockout matches in the 2018 World Cup sees the hosts take on a Spanish side that has yet to fire on all cylinders, while Croatia take their 100 percent record to face Denmark and Christian Eriksen. Here are some things to look out for on what promises to be a fascinating Sunday of football.

1. Can the Spanish hit top gear?

Spain topped Group B, but impressed few, especially their own press, with two disappointing displays against Iran and Morocco after kicking off with an entertaining 3-3 against Portugal. The fact that defender Sergio Ramos has completed more passes than anyone in the group stage says a lot about a side that saw a lot of the ball but didn't do much with it. However, they will hope that Russia will offer them more space than a defensive Iran did. If Russia do open up, the Spanish should have more than enough quality to beat them.

2. Will home comforts see Russia produce a surprise?

On paper, the host nation have a tough task to get past the Spanish, especially after Uruguay exposed their weaknesses in their last group match. However, Russia can expect help from the 81,000 fans in the Luzhniki Stadium and will also take heart from the fact Spain have never beaten a host nation in a major tournament. Their best hope will be to play a high-energy pressing game in their own half and look for Denis Cheryshev to exploit spaces behind a Spanish defense which tends to push to the halfway line.

3. Croatia's midfield to take out the Danes?

Croatia have passed their way into the last 16 with wins against Nigeria, Argentina and Iceland in which their midfield has given a clear indication of their quality. They need to take that momentum into the knockout stages, and will be favorites against a well-organized Danish side. Modric, Rakitic and Perisc will be at the helm for Croatia, who will look to Mario Mandzukic to lead their attack and Sime Vrsaljko to provide width down the flank.

4. Eriksen putting in the mileage

There is no doubt that Christian Erikson is the star for the Danish side, but while many focus on his passing skills and his delivery from set-pieces, they should also take a look at the ground he covers during a game. Nobody has run as far as Erikson's 36.42 kilometers so far in Russia and if his side are to keep Croatia at bay they will need to keep that workrate up to allow Erikson to work his magic down at the other end.