The first half had been a tale of two penalties, with Luca Toni converting from the spot before Jeremy Menez followed suit to draw Milan level.
Philippe Mexes was the unlikely scorer of what looked like being the winning goal shortly after half time, but instead of urging his men to push on, coach Filippo Inzaghi ordered a hasty retreat.
Milan inevitably came undone in the fifth minute of stoppage time as Uruguayan forward Lopez used his fresh legs to secure an unlikely Serie A point for 13th-placed Verona.
Victory would have fired the Rossoneri up to seventh, but they instead remain mired in mid-table.
In Saturday’s other game, Samuel Eto’o opened his goalscoring account for Sampdoria in a 2-0 home victory over Cagliari that boosted the Ligurian club into a share of fifth place.
The well-travelled striker swapped Everton for Serie A in January but had not made much of a direct impact for Champions League chasers Samp until Saturday’s second half of action at the Marassi.
Lorenzo De Silvestri’s header put relegation-threatened Cagliari on the backfoot before the break and the always-lively Eto’o put his new employers out of sight with a classy finish on 72 minutes.
The game was already beyond Gianfranco Zola’s visitors by the time defender Danilo Avelar saw red, and a third straight defeat leaves them three points adrift of 17th-placed Atalanta and safety.