Pretty much guaranteed, yeah. In 2017 the CDU and SPD both did about 4-5 points better in 1st votes than 2nd. In general, 1st votes don't tend to swing as much as 2nd votes, especially when incumbents are involved. There are a lot of constituencies where the 1st vs 2nd vote winners are different - a lot of SPD seats were like this in the last election. It's also how the AfD won the most 2nd votes in Saxony in 2017 but only 3 of 16 constituencies.