Inter followed up their win over closest challengers Juventus with a 4-2 victory at AS Roma last weekend, and they now have a seven-point lead with a game in hand after Juve lost at home to Udinese on Monday.
Friday's game at the San Siro should have seen Inter manager Simone Inzaghi come up against his brother, but Filippo was sacked by Salernitana last weekend after their 3-1 loss at home to fellow relegation battlers Empoli.
Fabio Liverani is now the club's third manager this season, and could not have been handed a more difficult start to what looks like an almost-impossible job of keeping the club in Serie A, an away trip to the league leaders.
When Inter and Salernitana met back in September, Paulo Sousa was in charge, and after the 4-0 defeat was followed by a 3-0 loss at Monza, he was replaced by Inzaghi after eight league games without a win.
Inzaghi managed two league wins in his time in charge, but Salernitana have only slipped further into relegation trouble and are now seven points from the safety zone with 13 points from 24 games.
One measure of the task facing Salernitana is the fact that they have scored 20 goals in 24 league games, while Inter's Lautaro Martinez has netted only one goal less in 21 matches.
Inter face Atletico Madrid in the Champions League next week, and the manager may be tempted to rest some of his players in the league, but Inzaghi can't afford to take the three points for granted against a desperate side with a new manager.
Juventus now find themselves looking over their shoulder, as AC Milan are just one point behind. After the 1-0 loss to Udinese, they take on another struggling side when they travel to face Hellas Verona on Saturday.
Before Monday's defeat, Juve had lost just once this season. However, after two consecutive defeats they have lost touch with Inter while Milan have edged ever closer.
Milan have gone nine league games undefeated, including the 1-0 win over Napoli last weekend, and they are away to nearby Monza on Sunday.
Atalanta are in fourth place after four consecutive wins, level on points with Bologna, and they host Sassuolo on Saturday, a side without a win in four games which has left them 17th, one point above the relegation zone.
Bologna's early season promise looked to have petered out after a run of four games without a win, but they have won their last three, including a midweek 2-0 victory over Fiorentina, and they are away to Lazio on Sunday.
Daniele De Rossi's perfect start at Roma was brought to an end by Inter, leaving his side four points off Atalanta in sixth, and they are at Frosinone on Sunday.
Defending champions Napoli, ninth in the standings, host Genoa on Saturday.
