The game went ahead only after groundsmen cleared the San Paolo pitch of snow. Lombardo, signed last month from Crystal Palace, had already marked his Cup debut with a fine goal in Lazio's 5-2 defeat at Internazionale, but his first league goal owed more to luck. The home goalkeeper, Francesco Mancini, came racing out of his area to clear the ball and miskicked, leaving Lombardo with a simple tap-in.
Vieri increased Lazio's advantage with a powerful shot after a defensive slip let in Marcelo Salas. After half-time Peter Knudsen pulled one back for Bari but, on the break, the irrepressible Vieri beat Mancini in the air to head home.
"This side can win the league title," Lombardo said. Lazio remain three points behind Fiorentina, whose 3-0 victory over Vicenza featured Gabriel Batistuta's 18th goal of the season.
Third-placed Milan stay five points adrift of Fiorentina, after coming from behind at San Siro to beat Salernitana 3-2. Parma dropped to fourth after needing an 86th-minute goal from Enrico Chiesa to force a 2-2 home draw with lowly Venezia.
The Italian international goalkeeper Angelo Peruzzi saved a second-half penalty from Roberto Muzzi, but he could not prevent the champions, Juventus, from a 1-0 defeat at Cagliari. Juve are now 14 points behind the leaders in seventh place.
Inter, the scorers of 10 goals in their last two matches, were without three forwards in Ronaldo, Ivan Zamorano and Nicola Ventola - all injured - and were held to a 0-0 draw at Piacenza.
Barcelona took back top place in Spain last night as they overcame Racing Santander 3-2 to make it six Primera Division wins out of six. Frank de Boer scored his first goal since moving from Ajax but was later sent off.
With both sides down to 10 men and eight minutes left, a surging run on the right by Luis Figo produced a drifting cross that Philip Cocu turned in to clinch the points for Barcelona. Louis van Gaal's side are a point clear of Valencia, who beat Atletico Madrid 2-1 away on Saturday.
The Dutch club, Feyenoord, are banning their own fans from European away games for the next year and a half. The decision to prevent foreign clubs from selling tickets to supporters of the Rotterdam club follows serious disturbances in the German town of Leverkusen after Saturday's friendly there.