Arsenal will feel they have got away with one against a Wolves side without a Premier League win this season.
The Gunners have struggled to break down teams that defend in a low block, and that again was the case as they failed to muster a shot on target in the first half.
Their performance lacked intensity, and with Wolves looking to slow the game down at every opportunity Arteta's side struggled to create chances.
It took Saka's excellent corner to force Johnstone into an error to open the scoring, and again a mistake from Mosquera for Arsenal to clinch all three points.
The home crowd were increasingly nervous - desperate for the title after three successive second-place finishes - and that tension transferred to the pitch as the Gunners retreated, trying to protect their lead.
They were almost made to pay, and with a late goal conceded against Aston Villa last week in the Premier League, supporters and Arteta would have feared the same fate.
Arsenal have been excellent for large parts of the season but have wobbled recently with draws against Chelsea and Sunderland and the loss to Villa in their past six league games.
Arteta is a demanding character and he and his squad need to find a way to deal with the pressure of a title challenge - the scrutiny and intensity will only grow as the season wears on.