Striker Luca Toni headed a goal in each half as Italy beat Scotland 2-0 in Bari, sending a clear message to the rest of Group B and to the critics of under-fire coach Roberto Donadoni.
The world champions looked sharp right from the start, despite not having played since a qualifying win over Georgia last November.
A friendly scheduled last month against Romania was cancelled in the wake of the death of a policeman in rioting after a Serie A match.
Italy are fourth on 10 points, but they are only two points behind the other three sides -- France, Scotland, who have played a game more, and leaders Ukraine.
Captained by Andriy Shevchenko, Ukraine were 1-0 winners over Lithuania, courtesy of an Oleg Gusev header.
Greece, rocked by a 4-1 home defeat by arch-rivals Turkey last weekend, beat Malta 1-0 with a 66th-minute penalty converted by Angelos Basinas, following a red card for Malta's Roderick Briffa.
The win moved the Greeks into second place in Group C on 12 points, one behind Turkey who came from 2-0 down to draw 2-2 with Norway in Frankfurt.
The Turks, playing behind closed doors in Germany to complete a ban after crowd trouble in a World Cup qualifier against Switzerland in 2005, were trailing with under 20 minutes to go before Hamit Altintop levelled with two free kicks.
Sweden, the only side other than Turkey with a 100 percent record before Wednesday's games, fared even worse -- losing 2-1 in Northern Ireland after taking a 27th-minute lead.
Johan Elmander got the opener but Northern Ireland striker David Healy, who scored a hat-trick against Liechtenstein on Saturday, struck twice more to propel Lawrie Sanchez's men to the top of Group F.
It is a remarkable achievement for both men.
Healy is now the qualifying competition's top scorer with nine goals while Sanchez has defied the odds with his team since being tipped to quit after he was savaged in the local media last September.
His team now have 13 points, one more than Sweden and four ahead of Spain, who gave their qualifying hopes a much-needed boost with a 1-0 win over Iceland that lifted them to third in the group.
Group E leaders Croatia, who did not play, now have three teams firmly on their tail with Russia, Israel and England all just two points behind.
Israel leapfrogged England after a 4-0 drubbing of Estonia in which 17-year-old substitute striker Ben Sahar scored twice.
England, who were booed at halftime and full time, stumbled to a 3-0 win over lowly Andorra in Barcelona -- with Steven Gerrard only breaking the deadlock in the 54th minute.
He added another before David Nugent tapped in a late third on his debut but it will not be enough to still a growing media campaign against coach Steve McClaren.
Furious fans chanted "What a load of rubbish" and "You're not fit to wear the shirt" as England toiled against a side ranked 163rd in the world.
The pressure appeared to take its toll on McClaren as he walked out of the news conference after just two minutes of questioning from reporters.
Giovanni van Bronckhorst kept the Netherlands top of Group G after scoring the winner five minutes from time in a 1-0 victory in Slovenia.
Though Northern Ireland's feat was impressive, the two real shocks of the night came earlier.
Azerbaijan defeated a previously unbeaten Finland side 1-0 in Group A to record only their third win in 34 qualifiers since they first started playing them in 1994.
Liechtenstein caused the next upset with a 1-0 victory over Latvia in Group F, bringing up only their second win in their 33rd qualifier since 1994.
With the qualifying competition now around the halfway mark, the next qualifiers take place at the beginning of June. Next year's finals are being jointly staged by Austria and Switzerland.