On 14 September, there was Norwich City 3-2 Manchester City. On 21 September, there was Manchester City 8-0 Watford. I'm excluding the CL win over Shakhtar Donetsk in between.
1971-72 Bundesiga Round 15: Eintracht Frankfurt 3:2 Bayern Munich Round 16: Bayern Munich 11:1 Borussia Dortmund
I have a candidate for the opposite scenario: 2010-11 Eredivisie Round 10: PSV vs Feyenoord 10-0 Round 11: Feyenoord vs VVV 3-0
From the so-called "Top 5" European leagues. Results of at least 9-goal margins that were sandwiched between defeats. First Division (ENG) 1891/92 Round 21: Blackburn Rovers 4-3 Aston Villa Round 22: Aston Villa 12-2 Accrington Round 23: Sunderland 2-1 Aston Villa First Division (ENG) 1892-93 Round 6: Newton Heath 2-4 West Bromwich Albion Round 7: Newton Heath 10-1 Wolverhampton Wanderers Round 8: Newton Heath 3-4 Everton First Division (ENG) 1930/31 Round 18: Birmingham City 2-0 Huddersfield Town Round 19: Huddersfield Town 10-1 Blackpool Round 20: Derby County 4-1 Huddersfield Town La Liga 1932-33 Round 9: Barcelona 4-0 Racing Santander Round 10: Racing Santander 9-0 Deportivo Alavés Round 11: Athletic Bilbao 9-5 Racing Santander La Liga 1949-50 Round 1: Athletic Bilbao 3-1 Barcelona Round 2: Barcelona 10-1 Gimnàstic Tarragona Round 3: Real Madrid 6-1 Barcelona La Liga 1949-50 Round 7: Athletic Bilbao 4-1 Celta Vigo Round 8: Celta Vigo 10-1 Gimnàstic Tarragona Round 9: Real Madrid 1-0 Celta Vigo La Liga 1950-51 Round 1: Valencia 3-1 Málaga Round 2: Málaga 9-0 Lleida Round 3: Alcoyano 2-1 Málaga La Liga 1953-54 Round 25: Racing Santander 4-3 Barcelona Round 26: Barcelona 9-0 Real Oviedo Round 27: Deportivo La Coruña 1-0 Barcelona Bundesliga 1971/72 Round 15: Eintracht Frankfurt 3:2 Bayern Munich Round 16: Bayern Munich 11:1 Borussia Dortmund Round 17: Schalke 1:0 Bayern Munich Ligue 1 1985/86 Round 26: Toulouse 2-1 Monaco Round 27: Monaco 9-0 Girondins Bordeaux Round 28: Nice 1-0 Monaco (It's never happened in Serie A)